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DEPARTMENT    OF   THE    INTERIOR 


MONOGKAPHS 


United  States  Geological  Survey 


VOLUME    XXXIII 


WASHINGTON 

GOVERNMENT    FEINTING    OFFICE 
1899 


CONTENTS, 


Page. 

Letter  of  transmittal xv 

Preface xvii 

Part  I. — General  geology  of  the  Naruagansett  Basik,  by  N.  S.  Shaler. 

Chapter  I. — Position  and  surface  relations  of  the  Narragausett  Basin,  and  the  roclis  it  contains.  7 

General  features 7 

Stratigraphical  and  orogenic  relations 10 

Results  of  the  action  of  orogenic  forces 20 

Overthrust  phenomena 25 

Dike  rocks  of  the  hasin 27 

Chapter  II. — Physical  history  of  the  hasin 30 

Relation  to  marine  and  atmospheric  erosion  and  deposition 30 

Age  of  Carhoniferous  rocks  of  tlie  basin 36 

Original  relation  of  the  Narragansett  Basin  to  the  sea 37 

Original  distribution  of  the  east  Appalachian  coal  field 38 

Ancient  margin  of  the  basin 40 

Relative  erosion  of  east  and  west  Appalachians 40 

Recent  changes  of  level 46 

General  statement  concerning  base-leveling 47 

Cycles  of  deposition , 49 

Arkose  deposits  of  the  basin 50 

Relation  of  arkoses  to  erosion 55 

Record  value  of  conglomerates 59 

Red  color  of  the  Cambrian  and  the  Carboniferous 62 

Chapter  III. — Glacial  liistory  of  the  Narragausett  Basin 64 

Carboniferous  conglomerates 64 

Last  Glacial  period 67 

Amount  of  erosion 71 

Chapter  IV. — Economic  resources  of  the  basin 77 

Soils 77 

Coals 79 

Condition  of  the  beds 80 

Characteristics  of  the  coals 82 

Conditions  of  future  economic  work 85 

Iron  ores:  Iron  Hill  deposit 88 

Part  II. — Geology  of  the  northern  and  eastern  portions  of  the  Narragansett  Basin. 
BY  J.  B.  Woodworth. 

Chapter  i. — The  jiroblem  of  stratigraphic  succession 99 

Repetition  of  lithological  characters 100 

Transition  of  lithological  characters 100 

Effects  of  igneous  intrusions 101 

Metamorphism 101 

Folding  and  faulting 101 

Denudation 101 

y 


VI  CONTENTS. 

Pakt  II — Continued. 

Chapter  I. — The  problem  of  stratigraphic  succession — Coutinuetl.  Page. 

Glaciatiou 102 

Suljraergeuce 103 

Absence  of  artificial  excavations 103 

Ch.ipter  II. — The  pre-Carbonlferous  rocks 104 

Algoulvlan  period 101 

Blackstone  series 101 

Cumberland  quartzltes 106 

Ashton  schists 107 

Smlthfield  limestones 107 

Cambrian  period 109 

Lower  Cambrian 109 

Middle  Cambrian  (unrepresented) 109 

Upper  Cambrian - 109 

Silurian  period  (unrepresented) ---  113 

Chert  pebbles - 113 

Chapter  III. — The  Igneous  rocks  of  the  border  of  the  basin 114 

Granitic  rooks 114 

Plympton  felsltes 116 

Granite-porphyry  117 

Other  rocks 117 

Gabbro  hills  of  Sharon 118 

Chapter  IV. — The  Carboniferous  basin 119 

General  structure  of  the  basin 121 

Maps  of  the  boundary  of  the  basin 124 

Boundary  of  the  basin  on  the  north  and  east 125 

From  Cranston  to  the  Blackstone  Elver 125 

From  Bl.ackstone  River  to  SheldonvUIe 127 

Connection  between  the  Narragausett  and  Norfolk  County  basins 127 

Sheklonville  cross  fault 127 

From  Sheldonville  to  Foolish  Hill 127 

Foolish  Hill  fault 128 

From  Foolish  Hill  to  Brockton 128 

From  Brockton  to  North  River 129 

Shumatuscacant  fault 129 

From  North  River  to  Lakeville 129 

From  Lakeville  to  Steep  Brook 130 

Inliers 130 

North  Attleboro  inller 131 

Nemasket  granitlte  area 131 

Summary 131 

Chapter  A'. — The  Carboniferous  strata 133 

Determination  of  horizons  within  the  basin 133 

Means  of  determining  superposition  ..." 133 

Tabular  view  of  the  strata  in  the  Narragausett  Basin 134 

Formations  below  the  Coal  Measures 135 

Pondville  group 135 

Basal  arkose  beds 135 

Foolish  Hill  exposures 135 

North  Attleboro  exposures 135 

Pierces  Pasture  in  Pondville,  Norfolk  County  Basin 135 

Absence  of  basal  granitic  conglomerates 136 

Geographical  conditions  indicated  by  the  basal  arkose 137 

Absence  of  Iron  oxides  In  the  basal  arkose 138 

Absence  of  carbonaceous  matter  .along  northern  margin 139 

Extent  of  arkose  zoue 139 


CONTENTW.  VII 

Part  II — Contiuued. 

Chapter  V.— The  Carboniferous  strata— Continued. 
Formatious  below  the  Coal  Measures— Continued. 

Pondville  group — Continued.  I'^ige- 

Suprabasal  conglomerates 1*'' 

Millers  River  conglomerate I'i" 

South  Attleboro  exposure ^"^^ 

Jenks  Park  exposure  in  Pawtucket I'll 

Wamsutta  group 

Bed  rock  areas  

Area  along  the  northern  border 1*'' 

Gray  sandstones  of  the  northern  border Hi 

North  Attleboro  area ^-^^ 

Conglomerates 1"*^ 

Sandstones ■*■* ' 


Shales 


147 


Central  Falls  area ^^'^ 

Pawtucket  area 

Red  beds  in  Attleboro,  Rehoboth,  and  Norton liS 

Norfolk  County  area ^*° 

South  Attleboro  limestone  bed 1^9 

Attleboro  sandstone _^ 

Igneous  associates  of  the  Wamsutta  group 152 

Diabase ^l^ 

Onnrtz-nornhvrv  aroup '■°^ 

155 


Diamond  Hill  quartz  mass 

Wamsutta  volcanoes ' ^^"^ 

Folding  of  the  Wamsutta  group 1='^ 

Flora  of  the  Wamsutta  group 1^8 

Coal  Measures 

Cranston  beds - 

162 


Providence  area 

Pawtucket  shales 


163 

ouuii-ainjo^*.- u  ot*iJiMou<jjjv,ij-  .----.-•----  ----  ----  ---- 

East  Side  area  iu  Providence ^^^ 

Teumile  Riverbeds 


AiCUaUOll  l»±ixii3  v:7.vjj0SUre -- -• -... 

East  Providence  area 


-tax 

Leonards  Corner  quarries '■^•^ 

Section  from  Watchemooket  Cove  to  Riverside 16o 

Halsey  Farm  section  at  Silver  Spring 166 

Exposures  in  Seekonk 

Hunts  Mills  section 1^^ 

Perrins  anticline 

Bored  well  near  Lebanon  Mills 1^^ 

Seekonk  beds - 

Seekonk  conglomerate '_ 

Beds  north  of  the  Tenmile  River  in  Attleboro 1^^ 

Contact  of  red  and  gray  beds,  with  local  unconformity 17b 

Red  shales 

Raindrop  imprints 

Attleboro  syncline 

Blake  Hill  fault  block ^°" 

Fossils ^g2 

Coal " 

Blake  Hill  thrust  plane ^°^ 

Dighton  conglomerate  group 


VIII  CO:i>fTENTS. 

Part  II — Continued. 

Chapter  V. — The  Carboniferous  strata— Continued.  Page. 

Extension  of  the  Coal  Measures  north  and  east  of  Taunton 187 

Dedham  quadrangle 187 

Mansfield  area 188 

Flora  of  Mansfield  section 191 

Bridgewater  area 192 

Abington  quadrangle 193 

Taunton  quadrangle 195 

Red  beds 195 

Outcrops  in  Norton 195 

Winnecounet  ledges 196 

Scolithus  beds 197 

Taunton  waterworks  section 198 

AVestville  section 199 

Taunton  River  Valley 200 

Middleboro  quadrangle 200 

Chapter  VI. — Organic  geology 202 

Insect  fauna 202 

Stratigraphic  position  of  the  fauna 203 

Odontopteris  flora 203 

List  of  plants  identified  by  Lesquereux 204 

Coal  beds 205 

Search  for  coal 207 

Thickness  of  the  Carboniferous 208 

Acknowledgments 211 

Appendix. — Bibliography  of  the  Cambrian  and  Carboniferous  rocks  of  the  Narragansett Basin.  212 

Part  III. — Geology  of   the  Carboniferous  strat.a.  of  the  southwestern  portion  of 

THE   NaRRAGANSETT   BaSIN,    VilTH  AN  ACCOUNT   OF   THE   CAMBRIAN  DEPOSITS,    BY 

Aug.  F.  Foerste. 

Chapter  I. — Introduction 223 

Difficulties  of  the  field  223 

Arrangement  of  report  225 

Chapter  II. — The  western  islands  of  the  bay 227 

Dutch  Island 227 

Conanicut  Island 228 

Fox  Hill,  Beaver  Head 228 

Northern  half  of  the  island,  north  of  Round  Swamp 229 

Southern  half  of  the  island,  soiith  of  Round  Swamp 232 

Shale  region 232 

Granite  area,  the  Dumplings,  and  the  arkose  region  west  of  the  Dumplings 233 

Hope  Island 235 

Prudence  Island 237 

Chapter  III.— The  western  shore  of  the  bay 242 

From  Saunderstown  to  Narragansett  Pier 242 

Along  the  shore 242 

West  of  the  cove  and  Pattaquamscott  River 246 

From  Saunderstown  to  AVickford 248 

From  Wickford  to  East  Greenwich 251 

AVestern  border  of  the  Carboniferous  basin,  from  East  Greenwich  to  Natick  and  northward 

into  Cranston 252 

Rocks  east  of  the  westernborderof  the  Carboniferous  area  in  Warwick  and  southern  Cranston.  256 

Warwick  Neck 258 

Chapter  IV. — The  northern  shore  of  the  bay 259 

Providence  River  and  eastward 259 

RumstickNeck 260 


CONTENTS.  IX 

Part  III — Continued. 

Chapter  IV. — The  northern  shore  of  the  bay — Continued.  Page. 

Popasquash  Neoli 261 

Bristol  Neclv 261 

Carboniferous  area 261 

Granite  area 262 

Warren  Necli 264 

Conglomerates  and  shales  of  S  wansea  and  Warren,  north  of  the  necks 264 

Gardeners  Neck 267 

Braytons  Point  and  northward 268 

Sewammock  Neck 268 

Chapter  Y. — The  eastern  shore  of  the  bay 269 

Steep  Brook 269 

FallEiver 270 

TownsendHill 270 

Tiverton 271 

Gould  Island 272 

Granite  area  at  the  northeast  end  of  Aquidneck  Island 273 

Eastern  border  of  the  Carboniferous  basin  south  of  Tiverton  Four  Corners 274 

Sandstone  series  between  Windmill  Hill  and  the  cove  north  of  Browns  Point 275 

Coarse  conglomerate  series  along  the  east  shore  of  Sakonnet  River 278 

High  Hill  Point 278 

Fogland  Point 278 

Exposures  west  of  Nonquit  Pond 279 

Exposures  between  Tiverton  Four  Corners  and  the  northeast  side  of  Naunaquacket  Pond .  280 

Little  Compton  shales 281 

Chapter  VI. — Aquidneck,  or  the  Island  of  Rhode  Island,  with  the  islands  of  Newport  Harbor. . .  284 

Arkose  and  pre-Carboniferous  rocks  on  Sachuest  Neck 284 

Arkose 281 

Pre-Carboniferous  rocks 286 

Eastern  shore  of  Aquidneck  Island  as  far  south  as  the  second  cove  northwest  of  Black 

Point 288 

Coarse  conglomerates  and  underlying  sandstone  series  from  Black  Point  to  the  north  end 

of  Smiths  Beach 290 

Coarse  conglomerates  and  underlying  rocks  on  the  neck  at  Eastous  Point 294 

Paradise  coarse  conglomerates 295 

Paradise  Rocks 295 

The  Hanging  Rocks 298 

Pre-Carboniferous  area 300 

Isolated  conglomerate  exposures  near  Eastons  Pond  and  northward 303 

Miautonomy  Hill  and  Coasters  Harbor  Island  conglomerates 304 

Miantonomy  Hill 304 

Beacon  Hill 304 

Field  exposures  of  coarse  conglomerates 304 

Coddington  Neck 305 

Bishop  Rock 305 

Coasters  Harbor  Island 306 

Newport  Harbor  Islands 307 

Gull  Rocks 307 

Rose  Island 308 

Conanicut  Island 308 

Line  of  separation  between  Carboniferous  and  pre-Carboniferous  rocks 308 

Goat  Island  and  Little  Lime  Rock 309 

Fort  Greene 309 

Morton  Park  and  southward 309 

Northeast  lines  of  possible  faulting 310 

Carboniferous  rocks  along  the  Newport  Cliffs 310 


X  CONTENTS. 

Part  III — Continued. 

Chapter  VI. — Aquidueok,  or  the  Island  of  Rhode  Island,  etc. — Continued.  Page. 

Newport  Neck  and  southern  cliff  rocks 314 

Greenish  igneous  rock  in  the  cliffs  southwest  of  Sheep  Point 314 

Granite  area  at  the  south  end  of  the  cliffs 315 

Granite  area  on  eastern  Newport  Neck 316 

Greenish  and  purplish  argillitic  rock  of  middle  Newport  Neck 316 

Pre-Carboniferous  green  and  purple  shales  of  western  Newport  Neck 316 

Shale  series  from  Coddlngton  Cove  to  Lawtons  A'' alley 319 

Greenish-blue  shales  of  Slate  Hill  and  southward 320 

Shale  series  north  of  Lawtons  Valley 320 

Shore  exposures  north  of  Coggeshall  Point 320 

Portsmouth  mine  and  northeastward 321 

Line  of  exposures  three-eighths  of  a  mile  west  of  the  Newport  road 326 

Shale  series  at  Butts  Hill 327 

Green  shales  and  conglomerates  of  the  northern  syncline 327 

Green  shales  along  the  western  Newport  road 327 

Conglomerates 328 

Relations  to  Slate  Hill  shales 329 

Chapter  VII.— The  Kingstown  series 331 

Unity  and  lithological  character  of  the  Kingstown  sandstone  series 331 

Section  from  the  Bonnet  to  Boston  Neck 333 

Section  from  the  Bonnet  to  Hazard's  quarry  and  Indian  Corner 333 

Kingstown  series  in  southwestern  Cranston  and  western  Warwick 334 

Probable  thickness  of  the  Kingstown  sandstone  series  in  Cranston  and  Warwick  ...  336 

Warwick  Neck  exposures 336 

Exposures  on  the  western  islands  of  the  bay 337 

Thickness  of  strata  between  the  Bonnet  and  Dutch  Island 337 

Lithology  of  the  Dutch  Island  series 338 

Beaver  Head  section 338 

Total  thickness  of  the  Kingstown  series,  including  the  conglomerate  at  Beaver 

Head 338 

Western  shore  of  Conanicut 339' 

Eastern  shore  of  Conanicut 339 

Probable  folding  in  the  northern  part  of  Conanicut  Island 340 

Hope  Island 341 

Kingstown  series  exposures  on  the  western  islands 342 

Prudence  Island 342 

Western  Bristol  Neck 343 

Eumstick  Neck 344 

Kingstown  sandstones  equivalent  to  lower  part  of  Coal  Measures  group 344 

Triangular  area  of  the  Kingstown   series  in  the  Narragansett  Basin,  narrowing 

southward 344 

Thickness  of  the  series  and  evidence  of  folding 345 

Rocky  Point  conglomerate  and  its  connection  with  the  estimate  of  the  thickness  of 

the  northern  section 346 

Chief  features  of  the  Kingstown  series 346 

Fossil-plant  localities 347 

Chapter  VIII. — The  Aquidneck  shales 348 

Area  occupied  by  the  Aquidneck  shale  series 348 

Southern  Conanicut 349 

Prudence  Island 350 

Thickness  of  shale  series  on  each  side  of  the  Prudence  Island  syncline 351 

Bristol  Neck 351 

Aquidneck  Island 352 

Thickness  of  the  shale  section  east  of  the  Portsmouth  syncline 353 


conte:sts.  XI 

Part  III — Continued. 

Chapter  VIII.— The  Acxnidneck  shales — Continued.  Page. 

Probable  thickness  of  the  shale  section  west  of  the  Portsmouth  syncline 353 

Lithological  variations  in  the  shale  series 354 

Geological  structure  of  the  middle  third  of  Aquidneck  Island 354 

Strata  probably  folded 355 

Gould  Island  of  the  Middle  Passage 356 

Southern  third  of  Aqiiidneek  Island 356 

Upper  green  shales  of  the  Aquidneck  series 356 

Sakounet  sandstones  of  the  Aquidneck  series  west  of  the  river 357 

Thickness  of  the  uiiper  green  shales 357 

Thickue.ss  of  the  Sakounet  sandstones 358 

Northern  extension  of  the  Aquidneck  shales 358 

Equivalents  of  the  Kingstown  sandstone  and  Aquidneck  shale  series  northeast  of  Warren 

Neck 358 

Sakonnet  sandstones  on  the  east  side  of  the  river 359 

Absence  of  the  shale  series  beneath  the  coarse  conglomerates  east  of  the  Sakonnet  River. ..  360 

Wedge-shaped  areal  distribution  of  the  Aquidneck  shale  series 361 

Equivalence  of  the  Kingstown  sandstones  and  the  Aquidneck  shales 361 

Fossils  of  the  Aquidneck  shale  series 363 

Chapter  IX. — The  Purgatory  conglomerate 364 

Coarse  conglomerate  overlying  the  Aquidneck  shale  series 364 

Sakonnet  sandstones  within  the  Aquidneck  shales,  in  transition  to  the  coarse  con- 
glomerate    365 

Coarse  conglomerate  forming  the  latest  Carboniferous  rocks  in  the  southern  part  of 

the  Narragansett  Basin 365 

Purgatory  conglomerate  as  a  typical  exposure 365 

Identity  of  the  Purgatory  and  the  Sakonnet  Eiver  western  shore  coarse  conglom- 
erate    366 

Possible  syncline  between  the  two  western  Paradise  ridges  of  conglomerate 366 

Hanging  Rock  ridge,  possibly  the  eastern  side  of  an  anticlinal  fold 367 

Dips  immediately  east  of  Hanging  Rock  ridge 367 

Interpretation  adopted 367 

Southward  pitch  of  the  great  Paradise-Hanging  Rook  syncline 368 

Southward  pitch  of  the  Sakonnet  River  syncline 369 

Western  coarse  conglomerate  exposures 369 

Possible  syncline  immediately  west  of  Miantonomy  Hill 369 

Possibility  of  two  horizons  of  conglomerate  at  Miantonomy  Hill 370 

Interpretation  adopted 371 

Geological  position  of  the  Newport  Cliff  section 371 

Portsmouth  synclinal  conglomerate 373 

Conglomerates  of  Warwick  Neck  and  Swansea 373 

Thickness  of  the  coarse  conglomerate 373 

Fossil  localities 374 

Chapter  X. — The  arkoses  and  basal  conglomerates 375 

Natiok  arkose 375 

From  Natick  to  Cranston 375 

Base  of  the  Carboniferous  south  of  Natick 376 

Probable  relations  between  the  various  granites  and  pegmatites  and  the  Carbon- 
iferous beds 376 

Tiverton  arkose 378 

From  Steep  Brook  to  Nannaquacket  Pond 378 

South  of  Nannaquacket  Pond 379 

Equivalence  of  the  Tiverton  arkoses  to  those  near  Natick 379 

Sachuest  arkose '. 379 

Conanicut  arkose 380 

Rose  Island  and  Coasters  Harbor  Island  arkose 380 


XII 


CONTENTS. 


Part  III— Continued.  ^^S^- 

Chapter  XI.— The  pre-Carboniferous  rocks  of  the  southwestern  portion  of  the  Narragansett  Basin  381 

Little  Coniptou  and  Newport  Neck  shales 383 

Quartzitesof  Natick - ^^^ 

Chapter  XII.— The  Cambrian  strata  of  the  Attleboro  district 386 

Cambrian  brook  localities - ^^^ 

Localities  1  and  2,  southwest  of  North  Attleboro 388 

Valley  of  locality  3 392 

Locality  4,  northeast  of  Diamond  Hill - 393 

Maps  and  sections 

Index - 


394 
395 


ILLUSTRATIONS. 


Plate  I.  Landscape  looking  -svestward  across  the  upper  portion  of  Narragansett  Bay,  in  the 
lowland  of  the  Carboniferous  area,  to  the  base-leveled  area  of  mainly  crystalline 

and  pre-Carbonlferous  rocks 7 

II.  Pre-Carboniferous  rocks  at  western  border,  near  Providence,  Rhode  Island 126 

III.  Plant-bearing  outcrop  of  Wamsutta  group  in  North  Attleboro,  Massachusetts 146 

IV.  Faulted  diabase  dikes  in  North  Attleboro,  Massachusetts 152 

V.  Rocky  Hill,  Providence,  Rhode  Island,  a  glaciated  ridge  of  the  Carboniferous 162 

VI.  Carboniferous  sandstones  at  Silver  Spring,  Rhode  Island 166 

VII.  Carboniferous  sandstones  near  Attleboro,  Massachusetts 176 

VIII.  Medium-sized  conglomerate,  Attleboro,  Massachusetts 176 

IX.  Ripple-marked  vertical  sandstones,  Attleboro,  Massachusetts 178 

X.  Raindrop  Imprints  on  vertical  strata,  Attleboro,  Massachusetts 178 

XI.  Plainville  Valley,  Wrenthani,  Massachusetts 180 

XII.  Vertical  bed  of  Dighton  conglomerate  at  Attleboro,  Massachusetts 184 

XIII.  Near  view  of  Dighton  conglomerate,  Attleboro,  Massachusetts 184 

XIV.  Selected  waterworn  and  indented  pebbles  from  Dighton  conglomerate,  Attleboro, 

Massachusetts Igg 

XV.  Vertical  Carboniferous  sandstones,  Plainville,  Massachusetts 186 

XVI.  General  view  of  surface  at  AVest  Mansfield,  Massachusetts 188 

XVII.  Geological  map  of  the  northern  and  eastern  portions  of  the  Narragansett  Basin 210 

XVIII.  Contact  of  pegmatites  with  Kingstown  shales,  Watsons  Pier,  Rhode  Island 242 

XIX.  Coarse  pegmatites  of  Watsons  Pier,  Rhode  Island 244 

XX.  Cross-stratification  in  pebbly  sandstone  of  Kingstown  series.  Devils  Foot  Ledge,  Rhode 

Island 248 

XXI.  Sandstone-gneiss  of  Kingstown  series.  Devils  Foot  Ledge,  Rhode  Island 334 

XXII.  Stratification  and  slaty  cleavage,  Aquidneck  shales,  eastern  shore  of  Prudence  Island..  350 

XXIII.  Wave-cut  bench  in  Aquidneck  shales,  western  shore  of  Prudence  Island 352 

XXIV.  Fretwork  weathering  of  Aquidueclv  shales,  Prudence  Island 362 

XXV.  Pegmatite  dikes  cutting  Kingstown  shales,  Watsons  Pier,  Rhode  Island 376 

XXVI.  Hoppiu  Hill,  a  granite  mass  surrounded  by  Cambrian,  North  Attleboro,  Massachusetts.  384 

XXVII.  Sketch  map  of  the  North  Attleboro  Cambrisin  localities 386 

XXVIII.  Sections  in  the  Narragansett  Bay  region 394 

XXIX.  Sections  in  the  Narragansett  Bay  region 394 

XXX.  Sections  in  the  Narragansett  Bay  region 394 

XXXI.  Geological  map  of  the  southern  part  of  the  Narragansett  Basin 394 

Fig.     1.  Diagram  of  assumed  conditions  of  compressive  strain  in  rocks  in  a  basin  of  accumu- 
lation    49 

2.  Theoretical  plan  of  the  great  folds  of  the  Narragansett  Basin 27 

3.  Diagram  showing  misleading  synclinal  exposures  of  similar  strata 102 

4.  Exposure  of  disconnected  dike  in  Lime  Rock  quarries,  Rhode  Island 108 

5.  Sketch  map  of  distribution  of  upper  Cambrian  pebbles 410 

6.  Map  showing  distribution  of  metamorphosed  Carboniferous  rocks 120 

XIII 


XIV  ILLUSTRATIONS. 

Page. 

Fig.     7.  Map  showing  general  outline  of  the  Narragansett  Basin 121 

8.  Section  across  eastern  arm  of  the  basin 122 

9.  Outline  map  and  general  cross  section  of  the  northern  part  of  the  basin 123 

10.  Edward  Hitchcock's  cross  section  of  the  Carboniferous  area 123 

11.  Map  showing  distribution  of  red  sediments 142 

12.  Geological  section  northward  from  Robinson  Hill 145 

13.  Diagram  showing  disapjiearance  of  the  Wamsutta  group  in  the  Coal  Measures 148 

14.  Section  through  felsite  knob  in  Attleboro,  Massachusetts 153 

15.  Geological  section  in  the  Millers  River  region 156 

16.  Geological  section  in  the  Arnolds  Mills  region 157 

17.  Hypothetical  geological  section  cast  and  west  through  Providence,  Rhode  Island 160 

18.  Folded  and  faulted  Carboniferous  shales  at  Pawtucket,  Rhode  Island 162 

19.  Sketch  of  zone  of  excessively  jointed  sandstones,  face  of  McCormick's  quarry 166 

20.  Geological  section  from  Watchemocket  Cove  to  Riverside,  Rhode  Island 166 

21.  Geological  section  through  rocky  islets  at  Halsey  Farm,  Silver  Spring,  Rhode  Island. ..  167 

22.  Geological  section  of  rocky  headland  near  Silver  Spring,  Rhode  Island 168 

23.  Theoretical  section  of  folded  structure  on  western  margin  of  the  Narragansett  Basin..  169 

24.  Contemporaneous    erosion   with  unconformity  in   the    Carboniferous    at    Attleboro, 

Massachusetts 176 

25.  Diagram  showing  cross  bedding 178 

26.  Geological  section  of  Plain ville  Valley  and  thrust  plane 183 

27.  Section  of  the  Mansfield  Coal  Measures 190 

28.  ■  Geological  section  in  Westville,  Massachusetts 199 

29.  Diagram  illustrating  the  case  where  boring  affords  a  satisfactory  test  for  coal  Ijeds 208 

30.  Diagram  illustrating  the  case  where  trenching  affords  a  satisfactory  test  for  coal 208 


LETTER  OF  TRANSMITTAL, 


Department  of  the  Interior, 

United  States  Geological  Survey, 

Cambridge,  Massachusetts,  March  2,  1896. 
Sir:  I  have  the  honor  to  submit  herewith,  for  pubhcation,  a  report  on 
the  geology  of  the  Nan-agansett  Basin.  This  report  contains  the  result  of 
a  considerable  amount  of  work  done  by  me  or  undei  my  direction  since  I 
became  an  officer  of  the  Survey.  In  part,  however,  it  is  the  result  of 
studies  undertaken  before  that  connection  was  established.  The  object  of 
the  report  is  to  set  forth  the  results  so  far  attained  in  the  study  of  a  field 
which  presents  singular  difficulties  in  the  way  of  its  interpretation,  and 
which  will  require  the  observation  of  many  other  students  before  it  becomes 
thoroiTghly  well  known.  Since  the  preparation  of  the  report  was  under- 
taken I  have  been  ordered  to  extend  the  results  of  a  general  nature  there 
attained  to  other  similar  basins  on  the  Atlantic  coast.  On  this  account 
it  has  seemed  desirable  to  postpone  a  thorough  consideration  of  luany 
portions  of  the  subject  until  other  parts  of  the  Atlantic  coast  have  been 
examined. 

I  have  the  honor  to  remain,  very  respectfully,  your  obedient  servant, 

N.  S.  Shaler, 

Geologist  in  Charge. 
Hon.  Charles  D.  Walcott, 

Director  United  States  Geological  Survey. 


PREFACE. 


As  the  conditions  under  which  this  report  has  been  prepared  are  of 
importance  as  explaining  the  nature  and  scope  of  the  investigations  on  which 
it  is  based,  it  is  fit  that  they  should  be  briefly  stated.  In  1865  I  became 
interested  in  the  geology  of  the  Narragansett  Basin,  principally  for  the  reason 
that  it  afforded  a  convenient  district  in  which  students  from  Harvard  Uni- 
versity could  be  instructed  iii  certain  problems  of  field  geology  which  were 
not  well  presented  in  the  neighborhood  of  Boston.  A  number  of  the  frag- 
mentary results  thus  obtained  were  published  in  several  papers,  but  the 
greater  part  remained  unpublished.  With  the  extension  of  this  desultory 
work  a  general  idea  as  to  the  structure  of  the  basin  and  its  relations  to 
some  of  its  more  important  groups  of  strata  was  obtained.  In  com'se  of 
time  it  seemed  possible,  with  a  moderate  amount  of  labor,  to  prepare  a 
memoir  on  the  field  which  would  add  something  to  the  body  of  information 
concerning  the  area. 

About  ten  years  ago,  at  the  request  of  Maj.  J.  W.  Powell,  then  Director 
of  the  United  States  Geological  Survey,  I  undertook  to  devote  the  time 
which  could  be  spared  from  more  pressing  duties  to  the  task  of  completing 
this  monograph.  Experience  soon  showed  that  the  mass  of  detailed  work 
which  remained  to  be  done  was  so  large  that  it  would  be  necessary  to  asso- 
ciate other  persons  in  the  undertaking.  To  Dr.  August  F.  Foerste  was 
assigned  the  southern  or  bay  section,  and  to  Mr.  J.  B.  Woodworth  the  north- 
ern portion  of  the  field.  The  division  of  their  work  was  not  determined  by 
a  precise  line,  but  was  left  to  mutual  understanding.  Dr.  Foerste's  studies 
began  in  1887.  They  were  interrupted  after  a  few  months'  labor,  but  were 
resumed  in  June,  1895,  and  the  field  studies  were  closed  in  September  of 
that  year.  Mr.  Woodworth  has  from  time  to  time  been  employed  in  this 
field  since  June,  1891,  but  the  work  was  discontinuous  until  the  field  season 
of  1895. 

JVION  XXXIIT II  ■  ^V" 


XVIII  PREFACE. 

In  allotting  these  tasks  to  Messrs.  Foerste  and  Woodworth,  I  turned 
over  to  them  the  small  share  of  the  results  that  I  had  obtained  in  work 
on  this  field  which  seemed  likely  to  be  in  any  way  helpful  to  them. 
Those  contributions  were,  however,  so  limited  in  quantity,  at  least  as  regards 
the  difficult  matters  of  detailed  structure,  that  the  sections  of  this  mono- 
graph which  appear  under  their  names  are  essentially  their  own. 

A  considerable  range  of  facts,  especially  those  which  relate  to  the  inti- 
mate structure  and  the  metamorphism  of  the  rocks,  have  not  been  to  any 
extent  treated  in  the  following  pages.  This  omission  has  been  designedly 
made  for  the  reason  that  the  inquiries  necessarj^  to  a  consideration  of  these 
subjects  would  have  required  the  services  of  a  trained  petrographer  for 
a  long  time.  In  a  like  manner,  the  very  interesting  and  important  vegeta- 
ble remains  which  abound  in  certain  parts  of  the  Coal  Measures  have  been 
passed  by,  thoixgh  they  well  deserved  an  extensive  study.  Thus  it  has 
come  about  that  the  extremely  varied  rocks  which  border  the  Paleozoic 
stratified  series,  or  which  are  in  the  form  of  islands  in  its  areas,  are  not  dis- 
criminated according  to  their  lithological  varieties,  but  are  indicated  merely 
as  pre-Carboniferous,  and  the  paleontology  of  the  basin,  which  includes 
extremely  interesting  groups  of  fossil  insects  and  other  organic  remains,  is 
in  no  wise  presented.  These  and  other  omissions  deprive  this  monograph 
of  all  claims  to  being  a  full  account  of  the  geological  phenomena  of  the 
basin;  it  should,  indeed,  be  considered  as  a  contribution  only  to  the  strati- 
graphical  and  dynamic  history  of  the  area. 

Where  the  statements  of  my  collaborators  are  not  questioned  by  me  in 
footnotes,  it  should  be  understood  that  I  approve  of  them  as,  so  far  as  I 
can  see,  the  best  that  can  be  made  concerning  the  facts  with  which  they 
deal.  In  only  one  instance  has  conference  failed  to  bring  about  a  concur- 
rence of  opinion  concerning  any  question  of  moment.  This  is  in  relation 
to  the  value  of  the  division  which  Dr.  Foerste  has  termed  the  Kingstown 
series,  which  he  regards  as  distinct  from  the  Aquidneck,  which  overlies 
it.  To  my  mind  it  appears  to  be  only  a  local  thickening  of  the  last- 
named  series,  with  a  similarly  local  addition  of  sandstones.  The  dis- 
agreement is  not  only  in  relation  to  the  propriety  of  separating  these  two 
sets  of  rocks,  but  also  as  to  the  thickness  of  the  lower  series.  It  seems 
to  me  most  likely  that  the  apparent  increase  in  the  depth  may  be  reasonably 
explained  by  the  occurrence  of  rather  compressed  folds,  the  axes  of  which 


PEEFACE,  XIX 

have  not  been  identified,  they  being  hidden  either  by  the  waters  of  the 
bay  or  by  the  drift  covering  which  conceals  the  greater  part  of  the  surface 
of  the  islands.  Nevertheless,  as  Dr.  Foerste,  who  has  given  much  time 
to  the  problem,  remains  convinced  as  to  the  distinct  nature  of  this  series, 
it  is  proper  that  he  should  express  his  convictions  in  his  portion  of  the 
report.  The  matter  is  clearly  debatable,  with  the  probability  that  the 
truth  is  on  the  side  of  the  observer  who  has  the  closest  personal  familiarity 
with  the  field. 

It  may  here  be  observed  that  the  conclusions  of  this  report,  so  far  as 
they  relate  to  the  general  structure  of  the  basin  of  which  it  treats,  are 
most  novel  in  the  matter  pertaining  to  the  orogenic  history  of  the  field. 
The  judgment  as  to  the  nature  of  the  mountain-building  work  rests  in  part 
upon  observations — in  the  main  unpublished — which  I  have  made  in  other 
somewhat  similar  basins  that  lie  along  the  Atlantic  coast  from  Newfound- 
land to  North  Carolina.  The  general  proposition  that  the  basins  are  char- 
acteristically old  river  valleys  which  have  been  depressed  below  the  sea 
level,  filled  with  sediments — the  sedimentation  increasing  the  depth  of  the 
depression — and  afterwards  corrugated  by  the  mountain-building  forces, 
will  derive  its  verification  in  part,  if  at  all,  from  study  of  other  troughs  of 
the  Atlantic  coast.  It  may,  however,  fairly  be  claimed  that  the  facts  set 
forth  in  this  memoir  show  that  this  succession  of  actions  has  taken  place 
in  the  Narragansett  field. 

The  contributions  to  our  knowledge  respectmg  the  value  of  the  coal 
deposits  of  this  basin  are  not  so  great  as  might  well  be  expected  from  a 
careful  study  of  the  field.  The  truth  is  that  the  exploitation  of  the  coal 
beds  has  been  done  in  an  extremely  blundering  manner,  so  that,  while  a 
large  amount  of  money  has  been  expended  during  the  last  hundred  years, 
the  amount  of  information  which  has  come  from  it  is  very  small  and  has 
little  more  than  negative  value.  It  may  reasonably  be  hoped  that  the  facts 
set  forth  in  this  monograph,  and  advice  based  thereon,  will  serve  to  prevent 
other  profitless  mischances  in  mining  in  this  area,  and  make  the  next  work 
which  is  undertaken  decisive  in  its  results  as  to  the  value  of  these  very 
peculiar  coals. 

The  first  part  of  this  report  is  limited  to  the  discussion  of  certain  general 
topics  which  could  not  well  be  treated  in  the  special  reports  of  Messrs. 
Woodworth  and  Foerste.     This  has  necessarilj'  led  to  a  somewhat  incom- 


XX  PREFACE. 

plete  presentation  of  the  pi-oblems  which  the  basin  affords.  It  should 
furthermore  be  noted  that  the  party  under  the  charge  of  the  senior  con- 
tributor is  now  engaged  in  studying  other  basins  of  the  Piedmont  or  east 
Appalachian  section  of  the  coastal  district.  From  these  inquiries  it  may  be 
expected  that  there  will  come  a  report  concerning  these  peculiar  features  in 
the  geology  of  this  country.  It  therefore  did  not  seem  worth  while  to 
undertake  a  more  systematic  inquiry  into  the  Narragansett  field,  which 
would  demand  a  larger  comparison  with  neighboiing  fields  than  it  is  possible 
yet  to  make.  The  reader  may  also  remark  the  fact  that  there  are  but  few 
diagrams  in  the  text.  Owing  to  the  small  and  disconnected  character  of  the 
sections  which  could  be  obtained  in  this  basin,  it  has  been  found  impossible 
to  represent  diagrammatically,  in  a  precise  way  and  for  all  parts  of  the  area, 
the  relations  of  the  strata.  Under  these  conditions  diagrams  are  likely  to 
have  a  fictitious  value — to  assert  more  than  the  facts  warrant.  So  far  as 
possible,  the  pictorial  representation  of  the  phenomena  has  been  limited  to 
local  sections  and  reproduced  photographs.  It  will  also  be  noted  that, 
particularly  in  Dr.  Foerste's  report,  attention  is  called  to  a  great  number  of 
localities  Avhich  are  cited  in  evidence  of  the  conclusions  to  which  the  writer 
has  come. 

N.  S.  S. 


GEOLOGY  OF  THE  NARRAGANSETT  BASIN 

Part  L— GENERAL    GEOLOGY 

By   T^A-THANIEL    S0XJTH:G-A.TE;    SUTLER 
MON  XXXTTT 1  1 


CONTENTS, 


Page. 

Chapter  I. — Positiou  and  surface  relations  of  the  Narragansett  Basin,  and  the  rooks  it  contains.  7 

General  features 7 

Stratigraphical  and  orogenic  relations 10 

Results  of  the  action  of  orogenic  forces 20 

Overthrust  phenomena - 25 

Dike  rocks  of  the  basin 27 

Chapter  II. — Physical  history  of  the  hasin 30 

Relation  to  marine  and  atmospheric  erosion  and  deposition 30 

Age  of  the  Carboniferous  rocks  of  the  basin 36 

Original  relation  of  the  Narragansett  Basin  to  the  sea 37 

Original  distribution  of  the  east  Appalachian  coal  field 38 

Ancient  margin  of  the  basin 40 

Relative  erosion  of  east  and  west  Appalachians 40 

Recent  changes  of  level - 46 

General  statement  concerning  base-leveling 47 

Cycles  of  deposition 49 

Arkose  deposits  of  the  basin 50 

Relation  of  arkoses  to  erosion 55 

Record  value  of  conglomerates 59 

Red  color  of  the  Cambrian  and  the  Carboniferous 62 

Chapter  III. — Glacial  history  of  the  Narragansett  Basin 64 

Carboniferous  conglomerates - 64 

Last  Glacial  period 67 

Amount  of  erosion 71 

Chapter  IV. — Economic  resources  of  the  basin 77 

Soils - 77 

Coals 79 

Condition  of  the  beds 80 

Characteristics  of  the  coals 82 

Conditions  of  future  economic  work 85 

Iron  ores :  Iron  Hill  deposit 88 

3 


LLUSTRATIONS, 


Page. 
Plate  I.  Landscape  lookiDg  westward  across  the  upper  portion  of  Narragansett  Bay,  in  the  low- 
land of  the  Carboniferous  area,  to  the  base-leveled  area  of  mainly  crystalline  and  pre- 
Carboniferous  rocks 7 

Fig.  1.  Diagram  of  assumed  conditions  of  compressive  strain  in  rocks  in  a  basin  of  accumula- 
tion   19 

2.  Theoretical  plan  of  the  great  folds  of  the  Narragansett  Basin 27 

5 


GEOLOGY  OF  THE  NARRAGANSETT  BASIN. 

PART  I.-GENERAL  GEOLOGY. 


By  N.  S.  Shaleb. 


CHAPTER  I. 

POSITION  AND   SURFACE    RELATIONS  OF  THE   BASIN,  AND 
THE  ROCKS  IT  CONTAINS. 

GENERAL  FEATURES. 

The  field  which  in  this  monograph  is  termed  the  Narragansett  Basin 
consists  of  a  considerable  area  of  stratified  rocks  ranging  in  age  from  the 
base  of  the  Cambrian  to  about  the  later  stages  of  the  Carboniferous  period. 
The  eastern  margin  of  this  basin  extends  on  its  northeastern  side  to  near 
the  Atlantic  coast  in  the  neighborhood  of  Duxbury,  Scituate,  and  Cphasset, 
or,  in  this  section,  to  within  about  6  miles  of  the  sea.  Its  northern  border, 
including  the  small  Norfolk  Basin  in  the  area  of  Carboniferous  rocks,  lies 
in  contact  with  the  southwestern  wall  of  what  is  commonly  termed  the 
Boston  Basin.  On  the  west  the  area  is  limited  by  relatively  high  lands 
which  separate  the  trough  from  the  Worcester  syncline,  a  basin  which 
owes  its  consti'uction  mainly,  if  not  altogether,  to  mountain-building  action 
occurring  after  the  end  of  the  Cai'boniferous  period.  On  the  south  the 
Narragansett  Basin  is  partially  separated  from  the  sea,  at  least  in  those 
portions  of  it  which  are  above  the  water  level,  by  a  constriction  formed  of 
ancient,  highly  metamorphosed,  stratified  rocks  and  a  variety  of  intrusions, 
together  with  some  granitic  areas  which  are  probably  of  great  age. 

7 


8  GEOLOGY  OF  THE  NAflRAGAiSrSETT  BASIN. 

The  north-south  extension  of  the  Narragansett  Basin,  including  the 
related  area  of  the  Norfolk  Basin,  the  axis  of  its  greatest  length,  is  from 
the  southern  portion  of  Narragansett  Bay  to  near  Walpole,  a  distance  of 
about  50  miles.  The  east-west  diameter,  from  the  western  part  of  Cum- 
berland, Rhode  Island,  to  the  town  of  Scituate,  Massachusetts,  is  about 
30  miles.  Although  its  outline  has  many  ii-regularities,  which  will  be 
hereafter  described,  the  basin  has  in  general  a  rudely  curved  form,  concave 
on  the  southeastern  side.  The  sections  given  in  a  later  chapter  of  this 
report  show  that  this  trough  has  great  depth,  the  lowest  stratified  beds 
disclosed  on  the  margins  possibly  attaining-  in  its  central  portions  a  level 
of  from  10,000  to  15,000  feet  below  the  plane  of  the  sea.  The  sections 
also  indicate  that  the  correlative  anticlines,  at  least  those  in  the  western 
and  central  parts  of  the  field,  probably  had  in  their  original  form  an  eleva- 
tion comparable  in  amount  to  the  depression  of  the  great  trough  which 
they  inclose.  In  a  word,  the  facts  indicate  that  the  mountain-building 
work  effected  in  this  district,  and  altering  the  original  reliefs,  was  consider- 
ably greater,  and  gave  rise  to  sharper  foldings,  than  in  the  more  interior 
parts  of  the  eastern  coast  of  North  America,  where  the  elevations  still 
retain  the  mountainous  character. 

An  examination  of  the  structure  and  attitude  of  the  rocks  in  this 
basin,  as  will  be  shown  in  a  detailed  way  in  the  later  sections  of  this  rejjort, 
indicates  that  this  region  originally  contained  an  extensively  developed 
series  of  pre-Cambrian  rocks,  the  ag'e  of  which  is  not  yet  determinable. 
They  may  for  convenience  be  referred  to  that  limbo  of  ill-discriminated 
formations,  the  upper  Archean  (of  Dana),  or  Algonkiau.  Above  and 
probably  upon  the  eroded  surfaces  of  these  ancient  strata,  known  in  this 
report  as  the  Blackstone  series,  there  lie,  apparently  in  detached,  much 
worn  patches,  considerable  remnants  of  the  Olenellus  horizon,  or  the  lower- 
most stage  of  the  Cambrian.  On  top  of  this  formation  and  the  granites 
which  have  broken  through  it,  which  were  in  turn  much  degraded,  come 
the  Carboniferous  beds,  strata  which,  owing  in  part  to  their  great  thickness 
and  in  part  to  their  having  escaped  the  nearly  comjolete  destruction  which 
overtook  the  lower-lying  beds,  now  occupy  the  greater  part  of  the  basin. 

The  evidence  indicates  that,  on  the  western  border  of  the  basin  at 
least,  the  margin  of  the  field  was  determined  before  the  beginning  of  Cam- 
brian time.     At  the  beginning  of  the  Carboniferous,   there  is  proof  that 


GENERAL  FEATURES.  9 

along  the  eastern  border,  from  near  the  southern  end  of  Aquidneck  Island 
to  Freetown,  Massachusetts,  a  distance  of  35  miles,  a  granitic  area  of 
considerable  extent  had  already  risen  above  the  surface  of  the  sea  and 
was  the  seat  of  no  little  erosion.  This  is  shown  by  the  fact  that  along 
this  line  the  rocks  at  the  base  of  the  Carboniferous  section  are  made  up 
mainly  of  granitic  debris,  the  mass  forming  a  characteristic  arkose,  at 
points  so  resembling  the  material  from  which  it  was  derived  that  it  appears 
at  first  sight  to  be  the  product  of  simple  decay  in  place.  Its  age  is  suffi- 
ciently indicated  by  the  numerous  Carboniferous  fossils  disclosed  by  the 
pits  which  have  been  made  in  the  mass  in  the  search  for  fire  clays.  It  is 
likely — though  the  evidence  is  less  indicative  than  that  just  noted — that 
the  eastern  wall  of  the  basin  was  in  Carboniferous  time  continued  north- 
ward as  far  as  the  neighborhood  of  Cohasset.  The  evidence  is  to  a  great 
extent  from  the  drift,  and  is  therefore  subject  to  much  doubt. 

The  condition  of  this  basin  in  the  beginning  of  Carboniferous  time  was 
apparently  that  of  a  broad  trough  penetrating  far  into  the  land  and 
perhaps,  though  probably  not,  extending  westward  so  as  to  include  with- 
out break  what  is  now  the  separated  basin  extending  through  the  central 
part  of  Worcester  County  southward  into  Connecticut  and  northward  to 
New  Hampshire.  The  very  coarse  nature  of  the  pebbly — or,  indeed,  we 
may  term  it  cobbly — waste  which  occurs  in  the  upper  part  of  the  Carbon- 
iferous, appears  to  indicate  that  the  trough  must  have  been  shallow.  This 
conclusion  is  afiirmed  by  the  tolerably  uniform  distribution  of  the  pebbles, 
some  of  them  a  foot  or  more  in  diameter,  across  the  basin  on  the  line  from 
Fall  liiver  to  Attleboro. 

On  the  assiimption  that  the  Nai-ragansett  Basin  was  shallow  at  the 
beginning  of  the  Carboniferous  period,  and  on  the  supposition  that  in  the 
center  of  the  field  these  beds  attain  a  depth  of  several  thousand  feet,  it 
seems  necessary  to  assume  that  the  erogenic  work  was  in  part  accomplished 
during  that  time.  The  history  of  the  basin  can  be  best  explained  by  the 
hypothesis  of  an  extensive  subsidence  of  the  land  within  the  limits  of  the 
trough  as  the  beds  which  it  contains  were  laid  down,  and  a  corresponding 
overlap  invasion  of  the  sediments,  which  constantly  removed  the  shore 
lines  farther  away  from  the  center  of  the  basin. 

After  the  close  of  the  Carboniferous  period  the  Narragansett  district 
was  evidently  the  seat  of  yet  further  mountain-building  actions,  which  led 


10  GEOLOGY  OF  THE  NARRAGANSBTT  BASIN. 

to  extensive  dislocation  of  the  deposits  and  to  the  formation  of  several 
anticlines  and  synclines,  as  well  as  to  the  development  of  considerable  fault 
movements.  In  this  part  of  their  history  the  rocks  which  remain  in  this 
field  were  probably  deeply  buried  beneath  accumulations  which  have  been 
entirely  swept  away.  This  fact,  as  will  be  shown  in  detail  hereafter,  is 
indicated  by  the  large  amount  of  pebble  deformation  which  has  taken  place 
in  various  portions  of  this  field. 

Tlae  foregoing  statements  make  it  plain  that  the  detailed  consideration 
of  the  Narragansett  Basin  should  be  preceded  by  some  study  of  the  strati- 
graphical  and  orogenic  features  of  the  district  in  which  the  basin  lies. 

STRATIGBAPHICAL  AND   OROGEISTIC   RELATIONS   OF  THE  BASIN. 

The  relation  of  the  Narragansett  Basin  to  the  system  of  disturbances 
which  have  afiFected  the  eastern  coast  of  North  America  involves  certain 
questions  concerning  the  organization  of  the  Appalachian  system  which, 
so  far  as  I  am  aware,  have  never  been  considered  by  the  students  of  that 
field.  Those  mountains  are  generally  assumed  to  consist  in  part  of  an 
ancient  axis,  which  was  developed  perhaps  by  a  succession  of  movements, 
partly  in  Archean  and  partly  in  early  Paleozoic  time,  the  whole  forming  a 
range  extending  from  northern  Alabama  to  the  northern  parts  of  New 
England,  with  a  somewhat  obscure  continuation  through  Nova  Scotia  and 
Newfoundland  to  a  contact  with  the  old  Labrador  element  of  the  Lauren- 
tian  Mountains.  To  the  west  of  the  ancient  axis  of  disturbance  of  the 
Appalachians,  the  Allegheny  range  or  series  of  ranges  has  been  recognized 
as  a  development  which  took  place  after  the  close  of  the  Carboniferous, 
bringing  about  the  formation  of  some  score  of  considerable  folds,  all  of 
which,  except  those  in  the  extreme  south,  retain  their  relief  This  AUe- 
ghenian  division  extends,  with  diminishing  size  of  folds,  as  far  north  as 
near  Albany,  New  York  -^ 

West  of  the  Alleghenies,  throughout  their  whole  extent,  from  Alabama 
to  the  Mohawk  River,  there  is  a  table-land  which  manifestly  owes  its  uplift 
also  to  the  orogenic  work  that  resulted  in  the  formation  of  the  anticlines 
and  synclines  which  were  produced  to  the  west  of  the  old  axis  after  the 

'  It  is  characteristic  of  tlie  Alleghenian  division  of  the  Appalachians  that  it  consists  of  prevail- 
ingly long  folds,  which  are  much  compressed  and  generally  lie  in  such  a  position  that  an  ea-st-west 
section  of  the  field  traverses  four  or  five  of  the  similar  anticlines. 


strat[graphii;al  and  orogenio  relations.  11 

close  of  the  Carboniferous  period.  This  table-land  is  well  exhibited  in  the 
plateau  of  central  Tennessee,  but  is  most  strikingly  shown  in  the  degraded 
remnant  of  its  northern  part,  known  as  the  Catskill  Mountains. 

It  has  not  yet  been  sufficiently  recognized  that  to  the  east  of  tne  old 
Appalachian  axis  there  was  a  great  series  of  mountain  ranges,  now  obliter- 
ated, which  extended  from  the  southern  part  of  North  Carolina  along  the 
Atlantic  coast  as  far  as  Eastport,  Maine.  The  reason  why  this  portion  of 
the  system  has  been  neglected  is  found  in  the  fact  that  the  structures  which 
belong  to  it  are  peculiar  in  form  and  have  been  so  far  worn  away  that  they 
present  no  considerable  topographical  reliefs.  The  region  has  the  general 
character  of  a  country  which  has  been  brought  near  to  base-level,  and  the 
determination  of  the  position  of  the  ridges  and  furrows  can  be  made  only 
from  the  attitudes  of  the  rocks.  In  fact,  in  the  present  state  of  our  knowl- 
edge of  this  section  of  the  country,  only  a  few  of  the  old  troughs  are 
recognizable  and  the  position  of  the  folds  is  not  well  made  out. 

Beginning  on  the  south,  we  find  the  southernmost  of  these  folds,  so  far 
as  they  have  been  recognized,  in  the  Dan  River  Basin  of  North  Carolina. 
Farther  north,  the  Kings  Mountain  district  appears  to  indicate  the  seat 
of  another  folding,  a  part  of  the  rocks  involved  in  the  movement  being  so 
hard  that  they  have  not  yet  been  completely  eroded.  In  the  Richmond 
coal  field  an  extensive  series  of  beds,  probably  of  Triassic  or  Rhaetic  age, 
indicates  the  presence  of  another  considerable  basin,  which  has  something 
like  the  area,  depth,  and  general  form  of  the  Narragansett  downfold. 
From  studies  of  the  Richmond  Basin,  made  at  various  times,  I  have 
become  convinced  that  the  depth  of  the  depression  in  its  central  parts 
probably  exceeds  3,000  feet,  and  may  be  twice  that  amount,  and  that,  in 
part  at  least,  it  is  separated  from  the  sea  by  an  area  of  uplift  which  is  now 
worn  down  to  its  granitic  base. 

To  the  north  of  the  James  River  Valley  in  eastern  Virginia  the  Triassic 
rocks  are  again  found  involved  in  relatively  deep,  broad  troughs,  the  forms 
of  which  are  not  jet  well  made  out.  There  are  probably  several  of  these 
troughs,  some  of  which  contain  ancient  stratified  rocks  of  undetermined 
age  that  may  belong  in  pre-Paleozoic  time.  From  the  Potomac  River 
northward,  owing  to  the  mantle  of  Cretaceous  and  Tertiary  waste,  we  have 
no  distinct  indications  of  this  series  of  foldings  until,  in  New  Jersey,  we 
again  find  the  Trias  involved  in  troughs.     East  of  the  Hudson  the  broad 


12  GEOLOGY  OF  THE  NARRAGANSETT  BASIN. 

trough  of  the  Connecticut  Valley  may  be  regarded  as  in  its  nature  essen- 
tially equivalent  to  the  more  southern  basins,  the  only  substantial  difference 
being  that  on  both  sides  it  is  bordered  by  a  wide  field  of  high-lying  ancient 
rocks,  which  extends  eastward  nearly  to  Worcester  and  has  a  height  that 
is  not  found  in  the  case  of  the  walls  on  the  Atlantic  side  of  the  more  southern 
basins. 

At  Worcester  we  come  upon  the  most  southern  of  the  troughs  on  the 
eastern  side  of  the  central  Appalachian  axis  in  which  well-determined  Car- 
boniferous rocks  appear.  The  form  of  this  basin  is  not  well  known,  but, 
from  what  has  been  learned  concerning  it,  it  appears  to  be  relatively  narrow 
and  long,  having  in  general  a  closer  resemblance  to  the  synclines  of  the 
Alleghenies  than  any  other  of  the  troughs  in  the  group  which  we  will  here- 
after term  the  East  Appalachians.  The  Narragansett  trough  is  next  in  order, 
but,  as  it  is  to  receive  special  treatment,  it  may  here  be  dismissed  with 
the  brief  statement  that  in  its  type  of  form  and  in  the  nature  of  its  dis- 
locations it  differs  from  the  West  Appalachian  or  Allegheniau  series  of 
dislocations. 

North  of  the  Narragansett  district  we  have  in  the  Boston  Basin  a  con- 
siderable downfold,  the  axis  of  which  extends  in  a  prevailing  east-west 
direction,  the  depression  having  a  characteristically  great  proportionate 
width  and  an  irregular  form  which  belongs  to  the  other  East  Appalachian 
depressions. 

From  the  Boston  Basin  northward  the  complicated  and  imperfectly 
known  geology  of  the  country  indicates  a  succession  of  these  basins  dis- 
tributed along  the  coast  of  Massachusetts,  New  Hampshire,  and  Maine  to  the 
New  Brunswick  district.  One  of  these  occurs  at  Newburyport;  another  is 
traversed  by  the  Penobscot  River;  others  lie  between  Mount  Desert  and  the 
outer  Cranberry  Islands  and  to  the  north  of  the  Mount  Desert  Mountains ; 
yet  another,  or  perhaps  two  partly  separated  basins,  are  to  a  great  extent 
occupied  by  Cobscook  and  Passamaquoddy  bays ;  still  others  exist  along 
the  coast  of  Maine,  though  their  outlines  have  not  been  traced.  The  Car- 
boniferous areas  of  New  Brunswick  and  Nova  Scotia  appear  to  have  been 
preserved  in  basins  having  the  general  character  of  the  East  Appalachian 
troughs 

Reference  has  already  been  made  to  the  decided  differences  in  the 
forms  of  the  folds  which  occur  on  the  two  sides  of  the  old  Appalachian  axis. 


STRATIGEAPHICAL  AND  OROGENIO  RELATIONS.  13 

Those  on  the  west  are  narrow,  relatively  long,  and  consist,  with  slight 
exceptions,  of  simple  foldings  of  the  true  anticlinal  type.  Those  in  the 
eastern  or  seaboard  district  are  in  general  rudely  oval  in  form,  their  length 
usually  not  exceeding  twice  their  width.  They  are,  in  fact,  broad  troughs, 
the  included  strata  being  cast  into  a  number  of  anticlines  and  synclines. 
This  peculiar  difPerence  of  form  leads  naturally  to  the  sujDposition  that  the 
history  of  these  two  groups  of  depressions  has  been  diverse.  An  inspection 
of  the  deposits  verifies  this  supposition.  It  has  already  been  stated  that 
the  Narragansett  Basin  was  an  ancient  trough,  formed  before  the  Carbon- 
iferous period,  in  which,  during  a  process  of  subsidence,  the  beds  of  the 
Coal  Measures  were  accumulated.  The  evidence  derived  from  the  study 
of  the  Richmond,  the  Connecticut  River,  the  Boston,  the  Moimt  Desert, 
and  the  Passamaquoddy  basins  has  satisfied  me  that  the  troughs  are  of 
ancient  date,  that  they  were  filled  to  a  considerable  extent  with  materials 
imported  from  the  higher  country  about  them,  and  that  this  filling  process 
was  associated  with  progressive  local  subsidences. 

The  foregoing  considerations  seem  to  me  to  warrant  the  supposition 
that  the  East  Appalachian  basins,  or  at  least  the  greater  part  of  them,  were, 
in  the  beginning  of  their  formation,  erosion  troughs,  which  became  the 
seats  of  excessive  deposition,  and  this  brought  about  the  lowering  of  their 
surfaces  in  relation  to  the  original  bed.  In  a  word,  they  were  downpressed 
by  the  weight  of  the  burdens  which  came  into  them.  At  a  subsequent 
stage  the  mountain-building  forces,  acting  irregularly,  compressed  these 
troughs,  producing  the  sets  of  local  disturbances  which  are  exhibited  by 
each  field.  A  possible  instance  of  such  local  orogenic  action  in  very 
modern  times,  as  late  as  the  Pliocene,  is  found  in  the  tilted  strata  of  the 
Marthas  Vineyard  district.  In  this  case  excessive  deposition  of  a  local 
character  has  been  followed  in  turn,  first,  by  subsidence,  and  then  by  com- 
pressive action,  producing  a  large  measure  of  folding,  in  a  general  way  like 
that  which  has  taken  place  in  the  neighboring  Narragansett  Basin,  which 
lies  immediately  on  the  other  side  of  the  anticline  that  forms  the  eastern 
boundary  of  the  Narragansett  trough. 

It  should  be  said  that  the  hypothesis  of  the  antecedent  erosion  of  the 
basins  which  we  are  discussing  has  a  considerable  measure  of  support  from 
the  very  diverse  orientation  of  the  axes  of  the  East  Appalachian  troughs 
These  range  from  east  and  west  to  north  and  south,   a   diversity  which 


]4  GEOLOGY  OF  THE  NARRAGANSETT  BASIN. 

seems  to  me  to  be  inconsistent  with  the  supposition  that  they  have  been 
formed  through  the  action  of  such  accurately  determinate  strains  as 
produced  the  Alleghenian  ridges.  The  last-named  foldings  are  of  the 
normal  mountain  type.  The  axes  are  parallel  for  great  distances,  and 
where  the  ridges  change  their  orientation  they  preserve  their  parallelism 
and  alter  their  general  course  with  rather  gentle  curves.  They  exhibit  no 
case  of  such  contrast  in  the  axes  of  the  basins  as  is  shown  in  the  adjacent 
Narragansett  and  Boston  troughs. 

The  known  facts  concerning  the  effects  arising  from  the  accumulation 
of  thick  sediments  warrant  the  supposition  that  wherever  this  action  occurs 
it  is  likely  to  be  attended  by  a  subsidence  which,  though  of  a  local  char- 
acter, may  attain  an  extent  proportionate  to  the  influx  of  the  debris. 
Wherever  along  the  coast  line  long-continued  land  erosion  forms  deep 
valleys,  these  depressions  are  likely  to  be,  during  a  period  of  subsidence, 
the  seats  of  extensive  deposition.  Where  the  amount  of  this  sediment  is 
sufficient  to  develop  the  downcast  movement,  it  may  lead  to  the  formation 
of  a  trough  of  great  geological  depth,  though  it  may  at  all  times  be  shallow 
water  or  even  retain  the  state  of  a  delta  area.  It  therefore  does  not  seem 
a  matter  for  surprise  that  the  Atlantic  coast  district  should  exhibit  basins  of 
this  nature,  for,  although  this  coast  of  the  continent  has  been  subject  to 
many  alterations  of  level,  there  is  abundant  evidence  to  show  that  from  the 
Cambrian  period  to  the  present  day  the  eastern  front  of  the  land  has  been 
often,  indeed  we  may  say  prevailingly,  somewhere  near  its  present  position. 
There  has  been  ample  time  for  the  formation  of  many  great  coast  erosion 
troughs  and  for  their  filling  with  sediments  .to  the  amount  which  the 
hypothesis  requires.  The  final  development  of  anticlines  within  the  troughs 
in  the  extensive  way  in  which  they  appear  to  have  been  formed  may 
readily  be  explained  by  the  existence  of  the  same  compressive  tensions 
which  have  operated  in  the  West  Appalachian  field,  the  difference  being 
that  in  the  East  Appalachians  the  form  of  the  troughs  somewhat  controlled 
the  direction  of  these  anticlines,  while  in  the  western  portion  of  the  system, 
a  newly  emerged  part  of  the  continent,  they  appear  to  have  been  guided 
in  their  alignment  in  a  much  greater  measure  by  the  direction  of  the  com- 
pressive strains,  there  being  no  strong  topographical  features  except  the 
old  land  on  the  east  to  determine  the  trend  of  the  upcurving. 

At  the  present  time,  although  the  Atlantic  coast  of  North  America  has 


CONDITIONS  OF  DEPOSITION  OF  BEDS.  15 

been  subjected  to  recent  and  important  alterations  of  level,  there  are  many 
considerable  basins  along  its  shores  which  appear  t6  be,  in  their  structure 
and  history,  much  like  those  which,  according  to  the  hypothesis  we  are 
discussing,  were  developed  along  this  coast  line  during  the  Carboniferous 
period.  Albemarle  and  PamHco  sounds,  and  the  bays  of  the  Chesapeake 
and  Delaware,  need  only  a  continuance  through  a  considerable  extent  of 
geological  time  of  the  conditions  which  now  exist  to  bring  about  the 
formation  of  accumulations  essentially  like  those  under  consideration.  So, 
too,  certain  basins  along  the  Gulf  of  Mexico,  particularly  Mobile  Bay  and 
the  trough  of  the  Mississippi,  are  the  seats  of  extensive  estuarine  accumula- 
tions which  in  the  ages  to  come  may  take  on  much  the  same  aspect  as  the 
Narragansett  Basin. 

A  little  consideration  will  show  the  reader  that  a  river  valley  in  its 
lower  parts  naturally  becomes  the  seat  of  sedimentation.  An  inspection  of 
the  maps  of  shore  lines  will  make  it  plain  that  more  than  half  the  great 
rivers  of  the  world  have  the  lower  parts  of  their  valleys  flooded  in  a  way 
which  clearly  indicates  that  these  estuarine  regions  have  recently  been 
brought  beneath  the  level  of  the  sea  and  thus  converted  from  fields  of 
erosion  to  those  of  deposition.  The  generality  of  the  fact  that  the  great 
rivers,  notwithstanding  the  CAddent  tendency  to  accumulate  delta  deposits 
about  their  mouths,  enter  the  sea  through  their  own  submerged  valleys,  is 
probably  in  many  cases  to  be  accounted  for  by  the  fact  that,  while  the  con- 
tinental masses  as  a  whole  tend  rather  constantly  upward,  their  shores, 
being  near  the  seat  of  maximum  sedimentation,  naturally  tend  downward, 
in  the  manner  now  recognized  as  resulting  from  the  imposition  of  a  great 
load  of  sediments  on  any  part  of  the  earth's  surface.  We  may  therefore 
regard  the  occlusion  of  river  valleys  by  excessive  sedimentation,  which 
takes  place  coincidently  with  the  subsidence  of  the  trough  below  the 
level  of  the  sea,  as  a  normal  feature  in  the  history  of  any  shore  which  is 
intersected  by  river  valleys. 

If  the  hypothesis  which  is  here  adduced  to  explain  the  main  peculiar- 
ities of  the  East  Appalachians  be  established,  it  is  clear  that,  considered 
from  the  point  of  view  of  their  origin,  we  must  accept  a  new  specific  group 
of  mountains,  one  characterized  by  features  in  the  main  determined  by  the 
fact  that  the  beds  of  which  they  are  composed  have  been  laid  down  in  a 
formerly  existing  erosion  basin,  originally  due  to  stream  work,  though  it  may 


16  GEOLOGY  OP^  THE  NARRAGANSETP  BASIN. 

have  been  orographically  deepened  by  the  suosidence  caused  by  sedimenta- 
tion. It  will  be  seen  that  this  view  has  a  certain  superficial  resemblance  to 
the  hypothesis  commonly  known  as  James  Hall's,  in  which  mountains  are 
explained  by  supj)Osing,  first,  the  accumulation  of  a  thick  series  of  beds; 
second,  a  subsidence  of  the  crust,  due  to  the  deposits,  bringing  about  a 
folding  of  the  beds;  third,  a  massive  uplifting  of  the  foundation  on  which 
these  foldings  rest,  so  that  the  ridges  come  to  stand  on  a  lofty  pedestal.  I 
would  not  have  it  supposed  that  there  is  any  real  similarity  between  these 
hypotheses.  The  essential  difiiculty  of  the  hypothesis  which  endeavors  to 
explain  the  formation  of  mountains  first  by  subsidence  and  then  by  eleva- 
tion, is  that  there  is  no  sufficient  means  indicated  whereby  the  reelevating 
process  can  be  brought  about.  There  is  also  much  reason  to  question 
whether  the  downsinking  movement  could  develop  the  arches  of  the  strata. 
In  the  view  which  I  am  advocating,  the  conceptions  are  much  more  simple 
and  rest  upon  more  patent  facts.  The  steps  of  action  which  are  postulated 
are  as  follows:  First,  the  excavation  in  ancient  and  compact  rocks,  in  their 
nature  good  transmitters  of  thrusts,  of  a  trough  or  basin  such  as  is  likely 
to  be  formed  in  the  estuarine  section  of  a  considerable  river;  second, 
the  filling  in  of  this  basin  by  sediments  accumulated  during  a  downward 
oscillation  of  the  area  in  which  the  basin  lies;  third,  the  development  of 
compression  strains,  such  as  are  involved  in  rock  folding,  the  relief  being 
afforded  by  the  folding  of  these  stratified  deposits. 

If  this  hypothesis  as  to  the  origin  of  the  Narragansett  foldmgs  were 
correct,  we  should  ex^Dect  to  find  the  maximum  of  disturbance  in  the  extreme 
mai'gins  of  the  basin,  the  central  features  of  the  area  remaining  less  dis- 
turbed. As  will  be  seen  from  the  chapters  on  the  deposits  of  the  basin, 
this  is  essentially  what  we  find.  Wherever  the  area  is  of  sufficient  width 
to  afford  a  field  for  the  deA^elopment  of  the  structure  in  a  clear  way,  we 
observe  that  the  indications  of  lateral  stressing  are  very  clear  in  the  belts  of 
country  next  the  contact  with  the  crystalline  rocks,  while  in  the  central 
portion  of  the  field  the  beds  exhibit  lessened  stress.  Thus,  as  will  be  seen 
from  fig.  1  (p.  19)  and  the  sections  across  the  basin  where  the  distance  is  not 
far  from  20  miles,  we  find  the  marginal  portion  of  the  stratified  rocks  exceed- 
ingly flexed,  the  resulting  dislocation  attaining'  about  the  highest  order  of 
complexity,  while  the  intei'mediate  field,  including  much  more  than  one-half 
the  whole  length  of  the  indicated  line,  is  less  marked  by  the  stressing  forces. 


STEATIGRAPHICAL  AND  OROGENIC  RELATIONS.  17 

Where  the  Narragansett  Basin  narrows,  as  it  does  in  the  southern  third 
of  its  length,  the  type  of  the  folding  differs  somewhat  from  that  above 
indicated.  In  place  of  the  folds  on  either  side,  with  a  less  disturbed 
middle  field,  the  whole  of  the  section  is  folded  into  a  few  great  trough- 
shaped  undulations,  with  some  minor  irregularities.  Yet  the  fact  that  the 
strains  entered  the  bedded  rocks  from  the  sides  is  shown  by  the  character 
of  the  bottom  of  the  great  North  Aquidneck  syncline.  The  form  of  this 
part  of  the  basin  is  tolerably  Avell  known  by  the  mine  workings  in  the 
northern  part  of  Aquidneck  Island.  These  explorations  show  that  the  cen- 
tral portion  of  this  area  has  in  a  measure  escaped  the  disturbing  influences 
which  have  perturbed  the  beds  next  the  margins. 

Besides  the  evidences  of  stress  which  are  shown  by  the  extensive 
dislocation  of  the  stratified  rocks  of  the  Narragansett  Basin,  we  must  note 
the  equally  characteristic  marks  of  compression  afforded  by  the  interstitial 
movements  which  the  rocks  have  undergone.  These  changes  of  position 
of  the  rock  materials  are  exceedingly  common  in  the  metamorphic  part  of 
the  field  (see  fig.  6,  p.  120)  and  for  a  short  distance  to  the  eastward,  and  are 
readily  observed  wherever  there  are  any  data  by  which  they  may  be  judged. 
Wherever  the  rocks  lying  near  the  eastern  and  western  margins  of  the 
basin  contain  organic  fossils  or  pebbles,  save  of  quartz,  a  slight  examination 
will  in  practically  all  cases  show  that  those  bodies  have  been  more  or  less 
elongated,  the  direction  of  their  extension  usually  being  on  horizontal  lines 
which  are  approximately  parallel  to  the  neighboring  margin  of  the  basin. 
At  many  points  it  is  evident  that  the  elongation  of  the  pebbles  or  fossils 
has  been  as  much  as  50  per  cent  of  their  original  diameter  on  the  given  axis, 
and  sometimes  it  exceeds  this  amount.  It  commonly  happens  that  the 
distortion  Avas  sufficient  to  convert,  a  circular  disk  lying  in  the  axis  of  the 
movement,  and  having  a  diameter  of  a  foot,  into  an  ellipse  having  a  major 
axis  of  2  feet  and  a  minor  axis  of  6  inches.  In  rare  instances  the  alteration 
of  form  appears  to  go  much  beyond  this  proportion.  I  suspect,  indeed, 
that  at  a  few  points  it  is  obscurely  traceable  to  three  or  four  or  even  five 
times  the  original  length,  but  in  these  higher  terms  of  the  series  fossils 
become  mere  blurs  and  pebbles  lose  all  semblance  of  their  original 
character. 

Although  solid  bodies  like  quartzite  pebbles  may  often  be  found 
stretched  to  the  amount  of  50  to  100  per  cent,  it  is  generally  easy  to  see 

MON  XXXIII 2 


18  GEOLOGY  OF  THE  NARRAGANSETT  BASIN. 

that  the  matrix  in  which  they  are  embedded  has  been  much  more  extended 
than  the  more  I'igid  inchisions.  This  is  shown  by  the  fact  that  near  each  end 
of  the  axis  of  the  pebble  in  which  the  elongation  has  taken  place  there  is 
often  a  slickensided  surface,  showing  that  the  matrix  pulled  away  from  the 
sides  of  the  stone  and  slipped  by  them,  while  at  the  very  end  we  note  the 
existence  of  a  vein  deposit  which  is  also  slickensided  after  the  manner  of 
most  veins,  the  structure  showing  that  the  movement  which  pulled  the  matrix 
away  from  the  inclosed  fragment  operated  slowly  and  by  successive  steps. 
It  often  happens  that  pebbles,  especially  those  of  large  size  and  of  the  more 
rigid  varieties  of  stone,  show  no  distinct  signs  of  elongation,  and  yet  they 
have  these  appended  veins  and  the  slickensides,  indicating  that  the  more 
plastic  matrix  has  yielded  to  the  pressure  which  has  been  imposed  upon  it. 

Thei'e  are  certain  features  in  the  distribution  of  elongated  rock  masses 
which  appear  to  throw  some  light  on  the  questions  we  are  now  considering. 
In  the  first  place,  we  note  that  in  the  Narragansett  Basin,  and,  so  far  as  my 
observations  go,  iia  the  other  basins  of  the  East  Appalachians  as  well,  the 
plastic  migrations  of  the  strata,  as  shown  by  the  distortion  of  fossils  and 
pebbles,  are  decidedly  more  common  in  the  marginal  parts  of  the  several 
fields.  These  elongational  phenomena  are  strikingly  manifested  at  many 
points  in  the  southern  portion  of  the  Narragansett  area.  In  the  central 
part  of  the  area  there  are  extensive  tracts  of  conglomerate  where  a  close 
examination  has  failed  to  indicate  either  that  the  pebbles  were  stretched  or 
that  the  matrix  was  forced  by  these  inclusions.  This  goes  to  show  that  the 
force  which  affected  the  stratified  rocks  came  upon  them  as  a  thrust  hori- 
zontally transmitted  from  the  field  of  crystallized  rock  on  either  side. 

The  other  point  concerns  the  regional  distributions  of  plastic  migration 
of  rock.  This  phenomenon  seeiias  to  be  of  common  occurrence  in  the  East 
Appalachians  from  New  Brunswick  southward.  It  is  excellently  shown  at 
the  Cobscook  Basin,  about  Mount  Desert,  and  in  the  Boston  Basin;  in  the 
basins  to  the  southward  it  is  more  scantily  exhibited.  Curiously  enough, 
however,  this  feature  appears  to  be  prevailingly  lacking  in  the  rocks  of  the 
West  Appalachians,  notwithstanding  the  deposits  of  that  section  appear  to 
have  been  on  the  average  about  as  much  dislocated  by  folds  and  faults  as 
have  those  of  the  eastern  section.  It  is  not  clear  to  what  the  greater  plastic 
movement  of  the  eastern  rocks  has  been  due.  It  may,  however,  be  sug- 
gested that  sucli  movements  depend  upon  the  compression  of  rocks  while 


STRATIGRAPHICAL  AXD  OROGENIC  RELATIONS.  19 

Tinder  a  deep  cover  of  overlying  strata  and  therefore  at  temperatures  which 
woukl  in  a  large  measure  diminish  their  rigidity.  This  does  not  seem  a 
satisfactory  explanation,  for  the  reason  that  while  the  amount  of  strata  which 
has  been  removed  from  these  eastern  mountains  has  probably  been  larger 
than  is  the  case  with  the  western  ranges,  the  erosive  process,  at  many  points 
in  the  west,  has  gone  far  enough  to  reveal  the  bases  of  the  anticlines  and 
synclines,  even  as  it  has  done  along  the  Atlantic  coast.  It  has  been  noted 
that  the  eastern  basins  are  generally,  exce^it  perhaps  that  of  the  Dan  River, 
much  more  intersected  by  dikes  and  stocks  than  are  those  of  the  west,  where 
there  are  but  few  such  intrusions  known,  perhaps  in  all  not  over  a  dozen 
between  the  Catskills  and  Ala- 
bama, as  against  the  thousands 
which  may  be  traced  in  the  moun- 
tain-built area  of  the  Atlantic  coast. 

Xt  seems  reaSOnaDJe  to  assume  Fiq.  l. — Diagram  of  assumed  conditions  of  compressive  strain  i 

that     thp     PTtpnsivP     nln«^hV    mnvP-  rocks  in  a  basin  of  accumulation.    AA,  massive  crystalline 

inai      me     exieusive     piaSUO    move  ^ocks.    BB,  the  rocks  of  the  basins.    The  arrows  indicate  the 

mentS  of  the  rocks  in  tlie  East  Ap-  di™«t.ion  of  the  compressive  strains;  the  spaces  between  their 

i  heads  indicate  the  measure  of  the  yielding  at  the  several  points. 

palachian  district  are  related  to  the 

igneous  action  which  has  occurred  in  this  field,  and  that  the  two  groups  of 
facts  show  that  the  modes  of  action  of  the  mountain-building  forces  in  the 
two  districts  were  in  some  ways  very  different.  I  venture  to  suggest  that 
the  difference  was  partly  due  to  the  conditions  of  the  superficial  rocks  in  the 
two  fields.  In  the  west  the  surface  of  the  country  from  northern  New  York 
to  Alabama  was,  at  the  time  of  the  elevation  of  the  West  Appalachians,  again 
occupied  by  relatively  unbroken  strata  which  lay  on  the  surface  of  the  upper 
Paleozoic  rocks.  The  stresses  of  comjoression  which  assailed  this  wide  field 
when  the  conditions  of  resistance  were  uniform  affected  all  parts  of  it  in 
an  approximately  equal  degree.  In  a  limited  way,  in  northern  Alabama, 
Georgia,  and  Tennessee,  where  the  conditions  were  diversified,  the  stresses,  as 
shown  by  Hayes,  were  in  some  cases  locally  accumulated  and  so  discliarged 
as  to  bring  about  extensive  overthrusting ;  but  in  general  the  folding  was 
approximately  equal  for  each  unit  of  the  section  which  was  stressed.  There 
was,  in  a  word,  no  transfer  of  thrust  through  great  beams  of  massive  and 
therefore  unyielding  rock  to  fields  where  the  stress  could  take  effect  on  the 
easily  folded  strata  On  the  Atlantic  slope,  however,  the  conditions  led  to 
the  local  intensification  of  the  stress  phenomena.     Between  the  deep  basins, 


20  GEOLOGY  OF  THE  NAKEAGANSETT  BASIN. 

filled  with  their  bedded  rocks,  lay  fields  of  crystalline  materials  which  had 
been  compacted  by  previously  administered  presstu-es  and  the  accompany- 
ino-  metamorphism  until  they  had  been  In-ought  to  the  most  rigid  or  the 
best  thrust-transmitting  state  to  which  rocks  may  attain.  The  result  was 
that  the  compressive  strains  were  transmitted  through  these  ancient  close- 
knit  blocks  of  strata  to  take-  effect  on  the  frailer  materials  which  were 
inclosed  in  the  troughs  between  their  edges.  The  assumed  conditions  are 
in  a  diagrammatic  way  represented  in  the  accompanying  figure  (fig.  1). 

RESULTS  OF  THE  ACTIOI^^  OF  OROGENIC  FORCES. 

So  far  as  can  be  determined  by  the  evidence  which  has  been  found, 
the  orogenic  movements  which  flexed  and  fractured  the  Carboniferous  rocks 
of  the  Narragansett  Basin  did  not  affect  in  a  similar  manner  the  more 
ancient  formations  which  border  the  area.  There  are,  it  is  true,  certain 
faults  intersecting  the  margin,  particularly  on  the  northern  side  of  the  area, 
which  c\it  through  the  Carboniferous  beds  and  the  fundam.ental  complex 
alike,  but  there  is  no  evidence  that  these  faults  extend  very  far  beyond  the 
margin  or  that  folds  attended  the  formation  of  the  rifts.  Any  system  of 
anticlines  and  synclines  affecting  the  more  ancient  beds  would,  we  may 
fairly  presume,  have  left  their  marks  in  the  distribution  of  the  deposits  as 
they  appear  on  the  present  surface.  The  several  groups  of  metamorphosed 
beds  would  appear  in  parallel  bands,  an  arrangement  which  they  do  not 
exhibit. 

The  only  distinct  feature  in  the  ancient  compact  rocks  which  can  be 
attributed  to  compressive  action  is  the  system  of  shearing  planes  which 
have  been  extensively  developed  in  the  massive  rocks  on  the  margin  of  the 
basin.  Where  these  have  been  developed  in  the  granitic  rocks  they  have 
given  the  latter  a  gueissoid  aspect.  These  secondary  structures  are  most 
distinctly  marked  near  the  contact  borders  on  the  east  and  west,  and  appear 
to  diminish  as  we  pass  a  few  miles  from  the  present  margin  of  the  Carbon- 
iferous field.  The  existence  of  this  class  of  distortions  in  the  rocks,  along 
with  the  general  lack  of  evidence  of  folding,  points  to  the  conclusion  tliat 
the  pressure  affected  these  compact  formations  in  a  way  different  from 
that  in  which  it  affected  the  stratified  beds  of  the  basin.  It  may  be  tliat 
the  yielding  in  the  interstitial  movements  accomplished  a  certain  reduc- 
tion in  the  length  of  the  sections  even  when  the  materials  were  too  rigid 


EESULTS  OF  THE  ACTION  OF  OEOGENIO  FOECES.  21 

to  permit  them  to  take  on  the  normal  folds  which  afford  the  natural 
means  of  shortening  in  stratified  beds. 

Since  the  shearing  planes  of  the  massive  rocks  grow  less  evident  as  we 
go  away  from  the  margin  of  the  basin,  and  have  not  been  clearly  observed 
beyond  the  limits  which  are  likely  to  have  been  occupied  by  its  deposits, 
the  question  arises  whether  these  planes  are  not  a  consequence  of  the 
movements  which  must  have  occurred  in  the  rocks  that  lay  beneath  the 
Carboniferous  strata  at  the  time  they  were  folded.  That  some  form  of 
distortion  affected  these  basilar  dejDOsits  must  be  assumed,  but  the  jjrecise 
nature  of  the  movements  is  not  known. 

The  type  of  folding  exhibited  in  the  stratified  rocks  of  the  basin  is 
clearly  that  of  ordinary  synclines  and  anticlines  Avhich  have  been  carried 
to  a  rather  advanced  stage  of  development.  As  will  be  noted  from  the 
maps,  the  axes  of  these  folds  trend  nearly  north  and  south  in  the  southern 
portion  of  the  basin,  but  in  the  northern  part  they  incline  to  the  eastward, 
and  in  the  east  attain  a  position  nearly  at  right  angles  to  the  southern  folds. 
This  turn  of  the  structural  axes  seems  to  be  due  to  the  existence  of  the 
broad  eastern  bay,  which  is  a  notable  featiire  of  the  basin. 

There  is  another  noteworthy  feature  in  the  form  and  distribution  of 
the  anticlines  which  appears  to  be  closely  related  to  the  peculiar  history 
of  this  basin;  this  is  clearly  exhibited  in  the  accompanying  diagrammatic 
section  (fig.  2,  p.  27),  which  shows  the  attitudes  of  the  folds  in  the  central 
part  of  the  field  along  a  line  from  north  to  south.  In  this  section  the 
compressive  action  has  operated  to  create  strong  folds  next  the  borders  of 
the  basin.  These  folds  have  their  steepest  slojjes  toward  the  margin,  the 
sides  toward  the  center  of  the  basin  being  much  less  inclined,  so  that 
by  erosion  of  the  declivities  of  the  anticlines  on  either  side  a  relatively 
broad  trough  is  formed  in  the  central  part  of  this  field.  So  far  this  relation 
of  the  slopes  of  the  upper  folds  to  the  margins  of  ancient  massive  rocks  has 
been  distinctly  traced  only  in  the  northern  half  of  the  mountain-built 
district,  but  there  are  indications  that  it  exists  also  in  the  southern  portions 
of  the  field,  being  there  concealed  by  the  waters  of  the  bay  or  masked  by 
the  prevailing  covering  of  drift. 

The  disposition  of  the  strata  as  above  noted  appears  to  require  the 
supposition  that  the  thrust  acted  from  either  side  in  such  a  manner  that  the 
central  portion  of  the  basiii  was  a  relatively  neutral  zone  in  the  vaulting 


22  GEOLOGY  OP  THE  NARRAGANSETT  BASIN. 

movements.  If  the  strain  which  produced  the  folding  was  of  equal  value  in 
all  parts  of  the  basin,  there  would  be  no  reason  why  the  resulting  arches  of 
the  strata  sliould  not  have  been  of  ui:iiform  declivity  on  either  side.  I  can 
best  account  for  the  facts  in  this  case  by  supposing  that,  while  the  contraction 
which  brought  about  the  mountain  building  may  have  acted  in  all  parts  of 
the  field,  a  large  part  of  the  stress  was  carried  through  the  lateral  girders  of 
indurated  massive  rocks  on  either  side  of  the  basin  rmtil  it  could  be  applied 
to  the  newly  formed,  distinctly  layered,  and  therefore  less  resistant  materials 
contained  in  the  old  Narragansett  Basin. 

The  horizontal  value  of  the  movement  which  was  taken  up  in  the  fold- 
ings of  this  field  can  not  as  yet  be  accurately  computed.  The  attitudes  of 
the  beds,  however,  indicate  that  it  amounted  to  2  miles  or  more.  The  con- 
ditions of  this  action  may  be  considered  as  such  that  the  surface  of  the  cen- 
tral part  of  the  disturbed  area  may  not  have  been  moved  except  down- 
Avardlv,  while  the  longitude  and  latitude  of  the  points  on  the  surface  on 
either  side  jvhich  were  affected  by  the  foldings  were  evidently  changed  in 
an  increasing  measure  as  we  depart  from  the  central  axis. 

The  depth  of  the  distinctively  stratified  rocks  in  the  basin  at  the  time 
the  mountain-building  work  was  done  can  not  well  be  reckoned  at  less 
than  that  of  the  existing  section,  but  as  this  region  has  been  subjected  to 
an  amount  of  erosion  competent  to  bring  the  anticlines  and  synclines  to 
about  the  same  level,  it  may  well  have  been  near  double  that  aniount. 
Therefore  we  may  assimie  the  depth  of  the  section  of  massive  rocks  which 
conveyed  the  thrust  from  an  extreme  area  on  either  side  to  the  deposits  of 
the  trough  as  not  less  than  2  miles. 

It  is  not  yet  clear  whether  the  mountain-building  action  which  has 
affected  this  basin  was  altogether  accomplished  after  tlie  latest-fonned  beds 
which  it  now  contains  were  accumulated.  The  factthat  all  the  sections  of  the 
Carboniferous  series  were  accumulated  in  shallow  water,  or  but  little  above 
its  level,  requires  us  to  suppose  that  the  trough  was  the  seat  of  a  nearly 
continuous  depression.  It  is  to  be  expected  that  the  downsinking  would 
have  been  accompanied  by  some  measure  of  compressive  movement.  So 
far,  however,  the  field  has  afforded  no  evidence  of  such  mountain-building 
work  done  during  the  subsidence  of  the  trough.  On  the  contrary,  the 
observations  are  most  reconcilable  on  the  supposition  that  the  whole  of 
the  strictly  erogenic  action  took  place  after  the  work  of  depression  was 


RESULTS  OF  THE  AOTION  OF  OROGENIO  FORCES.       23 

complete.  In  fact,  it  can  not  be  believed  that  there  was  any  distinct  rela- 
tion between  these  two  movements — that  of  general  downsinking-  and  that 
of  warj^ing  nnder  the  influence  of  the  lateral  thrusting. 

It  may  be  noted  that  the  conditions  of  mountain  building  in  this  basin 
resemble  in  a  general  way  those  of  the  Appalachian  district,  with  the  excep- 
tion that  in  the  latter  region  the  neutral  axis  appears  to  have  been  in  the 
line  of  the  ancient  belt  of  the  Blue  Ridge  or  its  equivalent  ranges  to  the 
north  and  south.  Against  this  central  ridge  the  thrusts  apparently  came 
from  the  east  and  west.  Moreover,  in  this  Appalachian  field  the  com- 
pressive action  seems  to  have  been  distributed  over  a  much  wider  section, 
with  the  result  that  the  amount  of  deformation  per  unit  of  length  in  an 
east-west  direction  was  much  less  than  was  the  case  in  the  Narragansett 
Basin.  The  folds  are,  on  the  average,  less  crowded  together,  and  the 
synclines  are  wider;  in  other  words,  the  evidence  goes  to  show  that,  in 
proportion  to  the  size  of  the  disturbed  area,  much  more  movement  was 
taken  up  in  folds  in  the  Narragansett  Basin  than  was  the  case  in  any  part 
of  the  West  Appalachian  field  of  disturbances. 

The  relation  of  the  mountain-building  work  of  the  Narragansett  Basin 
to  similar  action  in  the  neighboring  fields  is  a  matter  of  much  interest. 
There  are  three  of  these  areas  that  deserve  special  notice — the  Connecticut 
Valley,  Marthas  Vineyard,  and  Boston  Basin.  Of  these  three  regions  of 
mountain-building  action,  the  one  most  remote — the  Connecticut — is  in  all 
respects  the  most  unlike  the  Narragansett  Basin  in  its  orographic  features. 
In  the  Connecticut  Basin  we  have  what  appear  to  be  the  same  general 
antecedent  features  noted  in  the  Narragansett  Bay.  There  was  a  preex- 
isting valley,  which  was  deeply  and  rapidly  filled  by  detrital  materials.  It 
is  likely  that  this  accumulation  took  place  during  a  j)eriod  of  subsidence; 
it  evidently  occurred  after  the  deposits  of  the  eastern  trough  had  been 
formed,  and  under  conditions  which  led  to  the  extravasation  of  large 
amounts  of  lava.  When  the  Connecticut  Basin  was  subjected  to  compres- 
sive action,  the  yielding  was  by  the  rupture  and  shearing  of  blocks,  with 
little  trace  of  folding.  It  seems  most  probable  that  the  hypothesis  adduced 
by  Prof  W.  M.  Davis — which  is,  in  effect,  that  the  easily  fractured  planes 
of  the  basement  rocks  of  the  area,  which  are  composed  of  schists  standing 
at  a  high  angle,  induced  the  for^nation  of  faults  rather  than  folds — accounts 
for  the  departure  of  this  region  from  the  type  of  mountain  building  else- 


24  GEOLOGY  OF  THE  NARRAGAISrSETT  BASIN. 

where  to  be  observed  in  the  New  England  troughs.  In  a  measure,  the  dis- 
tinct folding  of  the  neighboring  trough  deposits  on  the  east,  occurring  where 
the  basement  beds  are  of  an  essentially  nonschistose  character,  seems  to 
bear  out  this  hypothesis. 

In  the  Mal'thas  Vineyard  area  of  distortions  there  is  no  indication  of 
a  trough.  There  are  no  ancient  rocks  rising  above  the  plane  of  the  sea.  It  is, 
however,  quite  possible  that  the  northwestern  border  of  the  basin,  if  we 
assume  such  to  have  existed,  was  in  the  bed  rocks  of  the  neighboring  main- 
land and  that  the  seaward  border  has  been  worn  away  by  marine  action  or 
lies  depressed  below  the  sea  level.  It  is  to  be  noted  that  the  prevailing 
axes  of  the  dislocations  on  Marthas  Vineyard  indicate  a  pressure  acting 
from  the  northeast  and  southwest,  with  resulting  foldings  Avhich  are  mainly 
aligned  in  a  northwest-southeast  direction,  or  approximately  at  right  angles 
to  the  usual  trends  of  the  Narragansett  and  other  folds  of  this  part  of 
the  continent.  Although  it  seems  to  me  probable  that  these  crumplings 
of  the  Cretaceous  and  Tertiary  beds  of  Marthas  Vineyard  Avere  formed  in 
a  trough  which  was  filled  in  these  ages,  the  evidence  on  this  point  is  not 
clear.  So,  too,  with  the  dislocated  deposits  of  Block  Island.  It  will  there- 
fore be  best  to  pass  these  areas  by  with  the  remark  that  the  forms  and 
trends  of  their  orographic  reliefs  differ  widely  from  those  of  the  older  dis- 
turbances, and  that  some  of  their  pecidiarities,  especially  the  faultings  and 
complications  of  their  folded  strata,  may  be  due  to  the  fact  that  the  move- 
ments occurred  near  the  surface,  without  the  restraint  which  is  imposed  on 
beds,  such  as  those  in  the  Narragansett  area,  compressed  while  under  a 
thick  mantle  of  deposits  which  have  since  been  removed. 

In  the  Boston  Basin  we  find  series  of  rocks  which  have  the  same 
general  character  as  those  in  the  Narragansett  Basin.  To  a  great  extent, 
the  rocks,  as  regards  their  structure,  are  fairly  comparable  to  those  in  the 
Narragansett  district.  Although  the  evidence  is  not  perfectly  clear,  it  goes 
to  show  that  there  was  the  condition  of  a  preexisting  basin,  which  was 
formed  sometime  after  the  horizon  of  the  pre-Cambrian,  and  which  received 
the  deposits  of  the  Roxbmy  conglomerate  period,  which  make  up  the  greater 
part  of  the  accumulations.  As  yet  the  age  of  these  conglomerates  and 
the  associated  rocks  is  not  determined,  a  most  assiduous  search  having 
failed  to  reveal  fossils  of  determining  value.  Therefore  it  is  not  possible  to 
fix  the  earlier  limit  of  the  disturbances.     Still,  the  immediate  contact  of  the 


OVERTHRUST  PHENOMENA.  25 

basin  on  the  north  and  south  and  the  approximate  parallehsm  of  the  axes 
of  their  foldings  appear  to  indicate  that  the  strains  took  effect  on  them  at 
approximately  the  same  time. 

Complicated  as  is  the  structure  of  the  Narragansett  Basin,  that  of 
Boston  Bay  is  yet  more  involved.  Although  some  minor  folds  may  be 
traced  in  it,  and  larger  arches  are  fairly  to  be  assumed,  the  area  as  a 
whole  appears  to  be  much  less  massively  and  continuously  flexed,  and 
more  faulted,  than  that  on  the  south.  It  is,  raoreo^^er,  far  more  generally 
penetrated  by  dikes  than  is  the  Narragansett  field.  Its  type  of  structure 
seems  to  be  between  that  of  the  last-named  basin  and  that  of  the  Connecticut. 
It  is  probably  owing  to  the  relatively  deep  erosion  of  the  Boston  Basin 
and  the  large  amount  of  faulting  in  the  erogenic  work  that  it  is  so 
difficult  to  recognize  and  determine  the  elements  of  folding  which  have 
existed. 

OVERTHRUST    PHENOMElSrA. 

The  phenomena  of  overthrusting  which  occur  in  the  development  of 
mountain  dislocation  ha-s^e  of  late  been  the  subject  of  much  profitable 
inquiry.  It  is  therefore  worth  while  to  examine  into  the  question  of  their 
occurrence  in  this  basin.  As  will  be  noted  in  the  sections,  the  only 
portions  of  the  field  where  accidents  of  this  nature  seem  to  be  indicated  are 
in  the  district  extending  from  near  Providence  to  the  northern  boundary  of 
the  basin.  The  reason  for  this  may  be  that  only  in  this  part  are  the 
attitudes  of  the  rocks  near  the  margin  sufficiently  disclosed  to  make  a  close 
interpretation  possible.  Particularly  in  the  region  about  the  Attleboros 
the  positions  of  the  dislocated  strata  favor  the  view  that  the  beds  have  been 
at  first  folded  and  then  thrust  over,  usually  toward  the  less-disturbed  centers 
of  the  stratified  rocks,  so  that  a  certain  amount  of  migration  of  the  beds  has 
been  brought  about.  How  far  this  has  led  to  the  disruption  of  the  folds,  so 
that  the  masses  which  have  changed  place  have  been  rent  away  from  the 
beds  of  which  they  originally  formed  a  part,  can  not  be  determined  from 
the  data,  now  in  hand. 

It  is  probable  that  the  original  margin  of  the  Carboniferous  rocks  in 
this  basin  was  farther  away  from  the  center  than  it  is  at  present.  The 
process  of  erosion,  which  has  attacked  the  massive  crystalline  rocks  of 
the  bouiidaries  as  well  as  the  stratified  interior  parts  of  the  trough,  has 
most  likely  lowered  the  whole  of  southeastern  Massachusetts  to  the  extent 


26  GEOLOGY  OF  THE  NAREAGANSETT  BASIK 

of  several  lumdrecl,  perhaps  to  the  depth  of  1,000  or  more,  feet,  the  result 
being  that,  as  the  old  bordering  walls  had  an  erosion  slope,  the  margin  is 
at  present  perhaps  some  miles  nearer  the  center  than  it  was  when  the  folding 
was  done.  It  has  also  been  noted  that  the  folding  and  other  evidences  of 
stressing  which  the  rocks  present  diminish,  except  on  the  northern  border, 
as  we  pass  from  the  margin  toward  the  interior  of  the  Carboniferous  area. 
These  considerations  lead  us  to  see  that  the  portions  of  the  beds  which  were 
most  dislocated  have  been  removed  by  the  erosion  process,  which,  as  is 
shown  by  the  planed-down  character  of  the  surface,  has  undoubtedly  been 
very  active  in  this  part  of  the  continent.  It  is  therefore  not  unlikely  that 
great  migrations  of  strata  took  place  at  the  time  of  the  disturbance,  the 
indications  of  which  have  been  entirely  lost  to  us  by  the  process  of  decay 
and  removal  of  the  beds  which  were  involved  in  the  movements.  In  a 
word,  the  zone  where  we  might  most  naturally  suppose  the  overthrusting 
actions  to  have  taken  place  has  in  large  part  disappeared,  at  least  so  far  as 
the  superficial  beds  are  concerned. 

From  the  conditions  presented  by  this  basin  there  is  reason  to  believe 
that  the  rupture  and  horizontal  displacement  of  folded  strata  would  be  more 
likely  to  occur  here  than  in  the  ordinary  instances  of  mountain  folding. 
Under  the  usual  circumstances,  where  the  contracting  impulse  afi^ects  a 
large  extent  of  country,  influencing  all  the  rocks  alike,  the  relief  effected 
bv  the  corrugations  of  the  strata  is  apt  to  be  eqiial  in  all  parts  of  the  area 
subjected  to  the  movement.  When,  however,  as  in  the  Narragansett  dis- 
trict, the  strains  were  most  applied  on  the  margins  of  the  field,  where  the 
tensions  developed  in  a  wide  extent  of  country  were  localized  in  a  narrow 
zone  of  relatively  weak  strata,  we  must  expect  the  highest  type  of  distortion 
and  rupture  that  occurs  in  mountain- folding  Avork. 

Such  overthrusting  as  has  occurred  in  the  Narragansett  Basin  appears  to 
a  great  extent  to  have  been  begun  by  folding,  the  arches  being  raised  to  a 
considerable  height.  These  arches  appear  to  have  collapsed,  as  all  com- 
pressed arches  tend  to  do. 

Overthrusting  action  appears  to  be  most  probable  in  the  region  between 
the  villages  of  North  Attleboro  and  South  Attleboro,  where  the  relation  of 
the  red  Wamsutta  series  to  the  gray  rock  on  the  south  requires  the  supposi- 
tion of  this  movement.     So  far  as  has  been  observed  in  the  few  traceable 


OVERTHEUST  PHENOMENA. 


27 


faults,  there  is  no  tendency  of  faulted  blocks  to  ride  over  one  another.  It 
can  readily  be  luiderstood  that,  inasmuch  as  this  region  has  been  subjected 
to  very  extensive  erosion,  overthi'usting  which  was  preceded  by  the  collapse 
of  the  folds  might  have  all  the  marks  of  its  former  existence  destroyed  by 
the  removal  of  the  strata  which  were  involved  in  the  movement. 

An  ideal  section  (fig.  2)  drawn  by  Mr.  Woodworth  through  the  three 
great  synclines  in  which  the  Dighton  group  appears,  including  the  Attleboro 
syncline  on  the  noi'th,  the  Grreat  Meadow  Hill  trough  in  the  middle  of  the 
basin,  and  the  Swansea  syncline  on  the  south,  exhibits  a  symmetry  in  the 
cross  section  which  is  further  evidence  of  the  simplicity  of  the  larger 
features  of  structure  of  the  central  part  of  the  basin.  There  is  along  this 
line  of  section  a  great  broad  syncline  in  the  middle  of  the  basin.  It  has 
nearly  symmetrical  slopes  with  relatively  low  dips.     The  synclines  parallel 


sy/7c///}e. 


Gt.Afeac/o<A/  ///// 
2yr>c/// 


S^vansea 
s/nc//'ne 


Fig.  2.— Tlieoretical  plan  of  tbe  great  folds  of  the  Narragaiisett  B: 


with  it  on  the  nortli  and  south  have  their  axial  planes  inclined  away  from 
the  middle  syncline,  or,  in  other  words,  the  sides  of  the  synclines  facing 
the  middle  area  are  nearly  vertical.  A  plane  lying  in  this  region  of 
folding  would  have  been  deformed  so  as  to  give  a  cross  section  like 
that  in  fig.  2.  lliere  is  in  this  case  no  prevailing  pitch  of  the  axial 
planes  to  or  away  from  the  ocean  or  an  older  land  mass,  but  rather  a 
symmetrical  deformation  of  beds  with  reference  to  the  middle  line  and  sides 
of  the  basin  as  it  now  exists. 


DIKE   ROCKS   OF  THE   BASIN. 

Although,  as  before  stated,  the  systematic  study  of  the  igneous  rocks 
of  this  area  has  not  been  undertaken,  there  are  certain  features  connected 
with  their  distribution  which  deserve  notice.  These  concern  the  areas  in 
which  the  intrusions  occur  and  the  portions  of  the  great  section  which  they 
traverse. 


28  GEOLOGY  OF  THE  NARRAGANSETT  BASIN. 

So  far  as  has  been  observed,  all  of  the  numerous  intrusions  occur  on 
the  marginal  portions  of  the  basin,  mainly  on  its  western  side  and  in  the 
prolongation  of  the  area  in  what  is  known  as  Norfolk  Basin,  a  field  which, 
as  elsewhere  noted,  is  not  much  considered  in  this  report.  The  eastern 
margin  of  the  area  is  not  so  well  revealed  as  the  western,  but,  as  will  be 
seen  in  the  detailed  descriptions  of  Messrs.  Foerste  and  Woodworth,  with 
the  exception  of  the  felsite  dike  in  Plympton,  no  intrusive  masses  have  been 
discovered  on  this  margin.  Dikes  also  occur,  as  indicated  in  Dr.  Foerste's 
reports,  on  the  southern  portion  of  the  field,  but  not  so  abundantly  as  on 
the  western  versant.  So  far  as  the  observations  go,  they  make  it  improb- 
able that,  in  general,  any  dike  attains  the  surface  at  a  point  more  than  2 
miles  toward  the  interior  from  the  border  of  the  Carboniferous  field.  An 
exception  to  this  statement  must  be  made  in  the  case  of  the  Wamsutta  field, 
where,  perhaps  owing  to  the  large  amount  of  disturbance  the  beds  have 
undergone,  dikes  are  found  at  a  distance  of  nearly  4  miles  from  the  western 
border. 

It  may  also  be  remarked  that  the  extended  study  of  the  rocks  in  the 
central  portions  of  the  area  has  shown  that,  while  dikes  may  perhaps  have 
penetrated  to  the  lower  parts  of  the  section,  there  is  no  evidence  afforded 
by  the  bare  rock  surfaces,  or  by  the  materials  of  the  drift  so  far  as  observed, 
which  would  lead  to  the  supposition  that  these  injections  penetrated  into 
the  zone  of  the  upper  conglomerates. 

Perhaps  the  most  interesting  group  of  what  appear  to  be  intrusive 
masses  is  that  of  the  pegmatites  which  occur  in  the  southern  portion  of  the 
western  margin.  As  we  go  southward  from  Providence  there  is  a  gradual 
increase  in  the  measure  of  metamorphism  to  which  the  Carboniferous 
strata  have  been  exposed.  The  observer  is  led  to  suspect  the  existence  of 
some  extensive  concealed  intrusion  which  has  applied  much  heat  to  the 
section.  These  indications  of  metamorphism  increase  until  they  attain  their 
maximum  in  the  portions  of  the  field  in  and  about  Boston  Neck  and  Tower 
Hill.  Where  the  alteration  of  the  strata  is  most  considerable— where, 
indeed,  those  beds  appear  as  ordinary  gneisses — we  find  extensive  pegma- 
tite intrusions,  which  penetrate  these  conglomerate  and  sandstone  gneisses. 
1  have  been  unable  to  determine  whether  these  intrusions  are  to  be  classed 
as  dikes  or  as  veins.  So  far  as  observed,  the  facts  hardly  warrant  the 
assumption  that  the  metamorphism  is  directly  due  to  the  incoming  of  the 


DIKE  ROCKS  OF  THE  BASIN.  29 

pegmatites,  biit  rather  lead  to  the  supposition  that  these  last-named  deposits 
have  been  derived  from  some  large  granitic  mass  intruded  into  the  basement 
rocks  of  the  section,  though  at  no  point  exposed  on  the  surface. 

The  facies  of  the  beds  in  the  region  about  North  Attleboro  makes  it 
appear  not  unlikely  that  volcanic  action  may  have  taken  place  in  this  por- 
tion of  the  held.  • 


CHAPTER    II. 
PHYSICAL    HISTORY  OF    THE    BASIN. 

RELATION  TO  MARIIVE  AND  ATMOSPHERIC  EROSION  AND  DEPOSITION. 

It  may  well  be  noted  that  tlie  degree  to  which  shore  land  basms,  such 
as  we  are  now  considering,  are  developed  is  in  general  determined  by  the 
amount  of  time  during  which  a  given  coast  line  has  remained  in  about  the 
same  position.  It  is  not  to  be  supposed  that  the  coast  level  remains  endur- 
iugly  the  same,  but  rather  that  in  the  repeated  oscillations  the  sea  does  not 
long  desert  a  given  field.  During  the  periods  when  the  area  is  relatively 
high  the  rivers  in  the  lower  part  of  their  courses  have  a  chance  to  develop 
those  wide  valleys  of  gentle  slope  which  are  characteristic  of  regions  that 
have  attained  very  nearly  to  the  general  base-level  of  erosion — i.  e.,  the 
average  position  of  the  sea  during  its  endless  variations  in  height.  In 
general  it  may  be  said  that  widi  valleys  next  the  shore  are  the  best  possible 
indications  of  a  relatively  long  continued  preservation  of  coastal  conditions 
in  the  region  where  they  appear.  The  Atlantic  coast  of  the  Americas 
affords  numerous  examples  of  these  broad,  nearly  base-level  valleys,  which 
have  been  formed  at  divers  times  in  its  history.  As  the  existence  and  the 
number  of  these  valleys  have  a  distinct  bearing  on  the  problem  in  hand,  it 
is  worth  while  to  give  a  brief  general  account  of  them,  at  least  so  far  as 
North  America  is  concerned. 

Along  the  Gulf  of  Mexico  there  are  half  a  dozen  of  these  considerable 
troughs,  of  which  those  of  the  Mississippi  and  Mobile  rivers  are  the  most 
characteristic,  or  at  least  the  best  known.  Both  of  these  valleys,  and 
probably  the  other  basins  along  this  coast,  are,  at  least  as  regards  their  lower 
parts,  of  relatively  modern  origin,  dating  probably  from  Tertiary  times. 
On  the  Atlantic  coast,  to  the  north  of  Florida,  there  are  again  a  number  of 
these  lately  formed  basins,  of  which  those  of  Albemarle  Sound  and  Chesa- 
peake and  Delaware  bays  are  the  largest  and  most  characteristic. 


STEITCTUEAL  DEPTH  OF  BASIN.  31 

North  of  Delaware  Bay,  and  thence  along  the  coast  to  Greenland,  the 
number  of  distinct  coast  erosion  troughs  increases  and  the  evidence  of  their 
great  antiquity  is  very  clear.  The  position  of  the  Newark  deposits  in  the 
Connecticut  Valley  makes  it  evident  that  this  region  was  an  eroded  basin 
as  far  back  as  the  Triassic  period.  The  Narragausett  Basin  owes  its 
excavation  to  actions  which  antedate  the  Carboniferous.  The  Boston 
Basin,  and  several  others  to  the  northward  along  the  shores  of  Maine,  may 
be  dated  back  to  the  Paleozoic  age.  Yet  farther  northward,  wide  valleys 
of  the  coastal-plain  type,  though  now  deeply  submerged,  are  indicated  by 
the  reentrants  of  the  Bay  of  Fundy,  the  Gulf  of  St.  Lawrence,  and  prob- 
ably by  the  great  system  of  embayments  of  the  Arctic  realm,  the  Greenland 
Straits  and  Hudson  Bay,  as  well  as  by  a  host  of  lesser  indentations,  which 
probably  mark  the  seat  of  long-continued  or,  rather,  frequently  repeated 
river  action  interrupted  by  periods  of  marine  invasion. 

It  will  be  observed  from  the  statements  made  in  this  report  that  the 
Narragansett  Basin  has  at  present  an  average  structural  dejith  of  probably 
not  less  than  7,000  feet  and  a  maximum  depth  of  12,000  feet;  that  is  to 
say,  the  downfolded  Carboniferous  rocks  and  the  beds  which  lie  beneath 
them  attain,  at  the  base  of  this  incline,  a  position  at  least  the  last-named 
distance  below  the  present  sea  level.  The  question  arises  as  to  how  much  of 
this  geological  depth  is  due  to  erosive  work  on  the  rocks  of  the  area  and 
how  much  to  actual  depression  preceding  or  connected  with  the  folding  of 
the  strata.  If  the  basin  originally  had  anything  like  its  present  depth,  we 
should  have  to  suppose  a  very  great  change  in  the  position  of  the  coast 
line.  If,  on  the  other  hand,  we  may  assume,  as  is  done  in  this  paper,  that 
the  basin,  as  regards  its  geologic  depth,  is  mainly  the  product  of  folding, 
and  that  the  movements  are  probably  due  in  the  main  to  the  accumidations 
of  deposits,  then  the  original  depth  of  the  basin  may  have  been  slight. 

The  evidence  seems  to  show  that  the  coastal  basins  of  the  Atlantic 
shore  owe  their  depth  to  three  more  or  less  associated  actions — to  river 
ei'osion,  to  downflexing  and  faulting  associated  with  the  accumulation  of 
strata  during  periods  of  subsidence,  and  to  the  massive  swing  of  the  conti- 
nent in  those  large  deformations  such  as  have  taken  place  in  recent  times, 
with  the  consequent  invasion  of  the  sea  into  the  valleys.  Two  of  these 
actions  are  local  in  their  nature;  the  third  involves  continental  or  perhaps 
wider  conditions. 


32  GEOLOGY  OF  THE  NAREAGANSETT  BASIN. 

It  should  be  said  that  the  mainspring  of  the  development  which  has 
taken  place  in  these  basins  is  the  crustal  strain  which  manifests  itself  in 
mountain  building.  Where  this  strain,  as  in  the  ordinary  conditions  of 
mountain  growth,  such  as  existed  in  the  West  Appalachians,  takes  effect 
on  uniform,  horizontal,  little  eroded  strata,  the  action  appears  to  result  in 
the  formation  of  elongated,  more  or  less  accurately  parallel  ridges,  such  as 
are  exhibited  in  the  Jura  or  the  Alleghenies.  Where,  on  the  other  hand, 
as  along  the  Atlantic  coast,  the  crust  is  composed  of  ancient  massive  rocks 
in  which  deep  valleys  have  been  excavated,  the  orogenic  strains  result  in 
the  deformation  of  the  patches  of  stratified  rocks  which  may  have  been 
accumulated  in  the  great  valleys  during  the  periods  of  subsidence. 

The  dislocations  of  the  Atlantic  coast  basins  clearly  indicate  that  the 
stress  which  has  caused  them  was  what  we  may  term  quaquaversal — that  is 
to  say,  it  has  acted  in  several  directions  around  the  greater  part  of  the  hori- 
zontal circle.  This  behavior  of  the  crustal  stress  is  quite  different  from  that 
which  we  find  exhibited  in  normal  mountains;  there,  as  before  remarked,  the 
relief  has  been  obtained  by  the  formation  of  ridges  and  furrows,  the  axes 
of  which  are  nearly  parallel  to  the  same  great  circle.  Although  the  amount 
of  this  parallelism  has  usually  been  much  exaggerated,  there  can  be  no  doubt 
as  to  its  substantial  existence.  HoAvever,  it  seems  unwarranted  to  suppose 
that  the  axial  relation  of  the  ridges  is  due  to  the  existence  of  a  strain  acting 
in  but  one  direction.  All  that  is  required  to  produce  the  result  is  either  a 
certain  predominance  in  the  value  of  the  strain  in  a  particular  versant,  or, 
what  comes  to  the  same  thing,  a  greater  tendency  to  yield  along  one  set  of 
lines.  Instances  of  this  may  frequently  be  seen  in  the  wrinkling  of  veneers 
or  in  sidewalks  which  have  been  covered  with  some  plastic  materials.  With 
a  simple  device  the  cream  on  a  pan  of  milk  may  be  made  to  show  the 
effects  of  the  same  general  principle,  where  the  giving  way  takes  place 
rectilinearly,  though  the  difference  in  pressure  in  the  several  axes  of  the 
circle  is  but  small.  Moreover,  even  in  the  most  nearly  parallel  mountains, 
there  are  generally  to  be  found  cross  folds  which  show  very  clearly  that 
the  strain  has  not  been  uniaxial. 

The  foregoing  considerations  lead  us  to  infer  that  the  diversity  of  axes 
in  the  elevations  produced  in  the  singular  group  of  antecedent  basin  folds 
which  we  are  considering  has  not  been  brought  about  by  a  class  of  strains 
dififeriuo-  as  resrards  their  distribution  from  those  involved  in  the  formation 


VARIATIOXS  OF  SEA  LEVEL.  33 

of  ordinai-y  mountains,  but  rather  through  the  opportunit}^  which  these 
diversely  shaped  and  irregularly  disposed  basins  have  afforded  for  the  ^-aried 
application  of  the  stresses. 

As  before  noted,  thS  evidence  derived  from  the  geological  history  of 
southeastern  Massachusetts  and  the  neighboring  portions  of  the  shore  to 
the  north\\^ard  as  far  as  the  Grulf  of  St.  Lawrence,  and  to  the  southward 
into  tlie  Carolinas,  shows  that  while  this  coast  line  has  been  subjected  to 
repeated  and  considerable  variations  of  level,  it  manifests  an  equally  clear 
tendency  to  return  to  about  its  original  position.  Beginning  with  the 
Cambrian  time,  we  find  reason  to  believe  that  this  region  was  coastal  at  the 
outset  of  the  Olenellus  epoch.  If  the  rocks  of  the  Roxbury  conglomerate 
be  of  the  Potsdam  period,  the  same  was  true  at  the  last  of  the  Cambrian 
stages.  It  is  again  the  case  in  the  Carboniferous,  in  the  Trias,  the  lower 
Cretaceous,  the  middle  Tertiar}-,  and  at  the  present  day.  Evidence  found  on 
the  coast  of  Maine  indicates  that  the  coast  in  that  part  of  the  field  was  also 
near  by  in  the  Devonian  period.  Thus,  in  eight  or  nine  of  the  great  periods, 
well  spaced  through  recorded  geological  time,  we  find  the  coast  of  this  dis- 
trict near  to  its  present  attitude.  As  the  action  of  erosion  during  the  periods 
of  elevation,  and  the  accidental  burial  beneath  later  deposits  of  portions  of 
the  strata,  are  likely  to  have  obliterated  much  of  the  record,  the  point  which 
we  are  endeavoring  to  make  appears  to  be  well  affirmed.  This  point  is  of 
evident  value  in  the  present  inquirv,  for  it  serves  to  show  a  reason  why 
extensive  erosion  valleys  are  characteristic  of  the  Atlantic  coast.  In  those 
phases  of  the  coastal  movement  in  which  the  land  has  been  above  the 
present  level  of  the  sea,  there  has  been  an  opportunity'  for  the  formation  of 
extensive  valleys  of  erosion,  which,  from  time  to  time,  with  the  downsinking 
of  the  shore  line  as  a  whole  and  the  downward  warping,  concomitant  with  . 
the  extensive  deposition,  have  had  a  chance  to  take  on  their  present  peculiar 
character. 

In  this  connection  it  should  be  noted  that  the  usual  tendency  of  shore- 
line changes  on  the  periphery  of  the  continental  fold  is  to  return  the  coast 
after  each  considerable  oscillation  to  somewhere  near  where  it  was  before. 
Elsewhere,  more  than  once,  I  have  called  attention  to  tlie  facts  that  within 
the  ordinary  growth  of  the  great  corrugations  on  the  earth's  surface  the 
movements  are  normally  those  of  downsinking  of  the  ocean  floors  and 
uprising  of  the  emerged  portions  of  the  continental  mass,  and  that  this 
MON  xxxiii 3 


34  GEOLOGY  OF  THE  NAEEAGANSETT  BASHST. 

movement  is  essentially  like  the  rotation  of  the  levei*  about  the  neutral  or 
fulcrum  point,  which  is  ordinarily  near  the  shore  line.  On  the  doctrine  of 
probability,  it  is  more  likely  to  fall  at  the  contact  of  land  and  sea  than  at 
any  other  point  in  the  length  of  the  rotating  are'a.  If  the  land  advances 
from  the  ancient  shore,  the  natiiral  result  is  an  increase  in  the  amount  of 
erosion  and  consequently  of  deposition  off  the  given  coast  line.  This,  in 
turn,  as  an  effect  of  the  loading,  tends  more  sharply  to  depress  the  region 
next  the  coast,  and  so,  in  time,  to  a  return  of  the  shore  toward  its  original 
position.  If,  on  the  other  hand,  the  sea  invades  the  land,  considerably 
narrowing  the  field  of  erosion,  the  supply  of  sediments  is  checked  and  the 
element  of  accumulating'  weight  which  makes  against  the  uprising  is 
proportionately  lessened,  with  the  resulting  tendency  of  the  district  to 
ascend  in  the  next  adjustment  of  the  crustal  stresses  which  are  involved  in 
continental  growth. 

So  far  as  I  am  aware,  the  mountainous  elevations  which  have  been 
formed  along  the  Atlantic  coast  appear  to  have  been  the  result  of  stresses 
which  have  acted  in  a  somewhat  continuous  manner  from  the  Cambi'ian  to 
near  the  present  day.  The  di.slocations  seem  to  have  occurred  in  these 
basins  as  early  as  the  first-named  time,  and  in  the  basin  of  Marthas  Vine- 
yard they  operated  perhaps  until  the  first  stages  of  the  last  Glacial  epoch. 
It  is  true  that  the  evidence  as  to  the  distinct  basin-like  position  in  which 
the  rocks  of  Marthas  Vineyard  lie  is  not  very  clear,  for  the  reason  that  the 
eastern  wall,  if  such  wall  existed,  is  now  below  the  level  of  the  sea;  but 
the  mountain-building  nature  of  the  disturbances  appears  to  be  unquestion- 
able, the  original  folds  having  had  a  geological  height  of  several  hundred 
feet,  though,  owing  to  the  soft  nature  of  the  strata,  they  have  now  been 
reduced  to  near  their  base-levels. 

It  is  a  notable  fact  that  in  these  erosion-basin  mountains  of  the  Atlantic 
coast  there  is  a  manifest  tendency  of  the  streams  to  return  again  and  again 
to  somewhere  near  the  paths  from  which  thejT-  have  been  displaced  by  the 
subsidence  of  the  areas  beneath  the  sea  or  by  the  corrugation  of  the  beds 
which  were  formed  during  these  periods  of  depression.  Thus  in  the  case 
of  the  basins  along  the  coast  of  Maine,  those  of  Boston,  the  Connecticut, 
and  the  set  about  the  Chesapeake,  streams  answering  to  the  original  agents 
of  erosion  now  occupy  their  ancient  sites.  It  is  evident  that  in  this 
particular,  as  in  many  other  features,  the  dislocation  areas  we  are  consider- 


ORIGIN  OF  SEDIMENTS.  35 

iug  differ  from  those  of  normal  moimtains.  In  the  last-named  group,  as 
has  been  often  remarked,  the  sti'eams  very  generally  come  to  occupy 
the  geological  highlands — the  crests  of  the  anticlines.  The  reason  of  the 
departure  from  the  general  rule  in  these  antecedent  basin  mountains  is  that 
in  them  the  rim  is  of  hard  rock,  while  the  central  portion  of  the  area  con- 
tains softer  materials. 

It  should  furthermore  be  noted  that  the  downsinkings  which  lowered 
these  valleys,  and  thus  afforded  the  opportunity  for  deposition,  were  not 
generally  so  extensive  as  to  induce  the  formation  of  normal  marine  deposits. 
After  the  beginning  of  the  Carboniferous,  indeed,  it  ma}^  be  doubted  whether 
the  submergence  beneath  the  level  of  the  sea  was,  until  Cretaceous  times, 
ever  great  enough  to  mantle  far  over  the  surface  of  the  country.  Apart 
from  the  local  downsinkings,  I  see  no  reason  to  believe  that  the  shore 
within  this  time  has  swayed  downward  or  upward  more  than  a  few  hundred 
feet. 

So  far  as  the  examination  has  been  carried,  the  seat  of  origin  of  the 
detrital  materials  contained  in  the  Narragansett  Basin  is  tolei'ably  well 
explained.  The  granitic,  trappean,  schistose,  and  other  rocks  represented 
in  the  conglomerates,  with  a  single  exception,  may  be  paralleled  from 
deposits  the  like  of  which  are  known  within  a  few  miles  of  the  margin  of 
the  basin.  The  exception — a  most  notable  one — is  in  the  case  of  certain 
quartzite  pebbles,  sometimes  containing  an  abundance  of  ill-preserved 
brachiopods.  These  quartzites  are  all  fine  grained,  hardened,  but  not 
greatly  metamorphosed,  and  of  a  hue  varying  from  blue  to  white.  The 
age  of  the  material,  as  determined  by  Walcott,  is  that  of  the  Potsdam 
sandstone. 

Pebbles  of  these  quartzites  plentifully  occur  in  the  upper  conglomerates 
of  the  Narragansett  series,  as  is  elsewhere  noted  in  this  memoir.  They  are, 
however,  best  known  from  their  occurrence  in  the  drift  deposits,  where  their 
presence  is  doubtless  to  be  explained  by  the  breaking  up  of  the  Carbon- 
iferous beds  in  which  they  formerly  lay.  On  the  northern  shore  of  Marthas 
Vineyard  they  can  readily  be  gathered  to  the  number  of  many  thousands, 
and  on  Cape  Cod  they  occur  less  plentifully  as  far  east  as  Highland  Light. 

As  the  pebbles,  so  far  as  observed,  are  always  small,  never  exceed- 
ing about  a  foot  in  diameter,  and  as  they  are  always  rounded  in  a  sub- 
spherical  form,  it  seems  clear  that  none  of  them  have  been  brought  into 


3(3  geoloCtY  of  the  is^aeragansett  basin. 

their  present  position  from  the  original  strata  by  the  action  of  the  last  ice 
period.  Forming,  as  the)'  do,  a  considerable  part  of  the  mass  of  conglom- 
erates in  the  Narragansett  Basin,  it  is  clear  that  they  were  derived  from  an 
extensive  field.  Their  condition  indicates  that  they  were  imported  from 
that  field  by  torrent  action.  Although  it  is  possible  that  these  quartzite 
deposits  originally  lay  over  the  country  to  the  westward  of  the  Narragansett 
Basin,  the  failure  of  the  beds  to  appear  round  the  periphery  of  that  area 
leads  to  the  supposition  that  the  district  whence  they  were  derived  lay  to 
the  eastward  of  the  trough,  perhaps  beneath  the  region  now  covered  by  the 
sea  This  supposition  receives  some  warrant  from  the  fact  that  these  peb- 
bles are  most  abundant  in  the  eastern  portion  of  the  basin,  while  they  seem 
to  be  almost  lacking  in  the  western  part.  The  existence  of  these  pebbles 
well  toward  the  extremity  of  Cape  Cod  appears  to  indicate  the  occurrence 
of  similar  deposits  beneath  the  waters  of  ^Massachusetts  Baj.  For  further 
details  concerning  the  origin  of  these  quartzite  pebbles,  see  Part  II,  by 
Mr.  Woodworth. 

AGE  OF  THE  CAKBONIFEr^OUS  ROCKS  OF  THE  BASIN. 

The  evidence  goes  to  show  that  from  the  earliest  stages  of  the  Pale- 
ozoic to  the  beginning  of  the  era  when  the  Carboniferous  beds  of  this 
district  began  to  be  laid  down  the  field  was  mainly,  if  not  altogether,  the 
seat  of  erosive  actions.  No  remnants  of  the  formations  between  the  lower 
Cambrian  and  the  Carboniferous  have  been  found  in  folds  which  exist  in 
the  basement  rocks  of  this  part  of  the  countr}^  The  fact  that  beds  of 
Cambrian  age  have  survived  at  several  points  in  the  Narragansett  Basin  in 
the  region  to  the  northward,  while  no  deposits  of  the  Silurian  or  Devonian 
horizons  have  been  identified,  leads  to  the  supposition  that  the  sediment- 
making  conditions  were  not  in  existence  at  the  time  these  beds  might 
have  been  laid  down.  The  researches  of  Lescpiereux,  a  digest  of  which  is 
given  by  Woodworth  in  Part  II,  make  it  eminenth'  probable  that  the 
Carboniferous  series  of  this  field  does  not  begin  with  the  lower  portion  of 
the  Coal  Measures,  but  with  the  upper  part  of  that  section.  Not  onl}^  are 
the  lower  limestones  and  the  Millstone  grit  lacking,  but  about  half  of  the 
measures  which  normally  contain  a  better  coal  in  the  district  west  of 
the  central  Appalachian  axis  are  also  lacking. 

It  should  be   observed  that  the  fossils  Avhich  afforded  the  basis  for 


SEPAEATIOX  FROM  THE  SEA.  37 

Lesquereux's  conclusions  were  obtained  from  beds  whicli  lie  at  2,000  to 
3,000  feet  above  the  base  of  the  Coal  Measures  as  f(iund  in  this  basin, 
and  that  the  beds  whence  his  fossils  were  obtained  do  not  extend  nearer 
than  2,000  to  4,000  feet  to  the  top  of  the  highest  remaining  beds  of 
Carboniferous  age  which  are  found  in  this  area.  It  is  of  course  possible 
that  the  lower  portions  of  the  section,  the  fossils  of  which  have  not  yet 
been  studied,  may  prove  to  belong  to  the  lower  Coal  Measures,  but  the 
essential  lithological  similarity  of  the  beds  below  the  upper  cong'lomerates 
makes  this  view  improbable.  So,  too,  the  lack  of  paleontological  evidence 
concerning  the  precise  age  of  the  upper  conglomerates  permits  the  suppo- 
sition that  they  may  belong  to  the  Permian  period. 

ORIGI^fAXi  REL,ATIOK  OF  THE  NARRAGAXSETT  BASIX  TO  THE  SEA. 

It  is  noteworth}^  that  no  trace  of  marine  fossils  has  been  found  in  any 
portion  of  the  Carboniferous  section  in  this  basin.  ]\Ioreover,  there  are  no 
limestone  pebbles  which  would  lead  to  the  suspicion  that  beds  of  this  origin 
had  ever  formed  a  part  of  the  original  sections.  A  few  limy  deposits  which 
occur  in  the  northwest  portion  of  the  area  appear  to  be  the  results  of  infiltra- 
tion, and  to  be  classable  as  veins.  When  we  consider  that  the  Carboniferous 
section  of  the  West  Appalachians  exhibits  evidence  of  frequent  intrusions  of 
the  sea,  the  question  arises  how  a  basin  having  the  stratigraphical  profundity 
of  that  of  Narragansett  Bay  could  have  been  developed  adjacent  to  the 
shore  line  without  having',  in  its  repeated  subsidences,  experienced  marine 
invasion.  At  the  present  time  the  bottom  of  this  basin  lies  several  thousand 
feet  below  the  plane  of  the  ocean  waters  which  penetrate  it.  Even  befo]'e 
the  mountain-building  movements  which  have  deformed  the  rocks  began, 
it  is  probable  that  the  basin  had  something  like  its  present  depth. 

The  conditions  of  the  basin,  as  above  noted,  lead  to  the  conclusion  that 
during  the  Carboniferous  period  it  was  continuously  separated  from  the  sea, 
and  therefore  had  the  character  of  a  lake,  or  perhaps  that  of  a  broad  river 
valley.  As  it  was  evidently  the  seat  of  very  considerable  drainage,  the  out- 
going water  might  have  excluded,  in  a  sufficiently  effective  way,  the  pene- 
tration of  the  oceanic  waters,  even  though  the  plane  of  deposition  was  laot 
much  above  the  marine  level.  When,  however,  we  consider  how  subject 
all  coast  lines  appear  always  to  have  been  to  oscillations  of  level,  it  seems 
most  reasonable  to  suppose  that  the  basin  lay  always  at  a  considerable 


38  GEOLOGY  OF  THE  NAERAGANSETT  BASIK 

height  above  the  coast  hne,  and  most  hkely  at  some  distance  inland  from  it. 
These  considerations  serve  to  support  the  hypothesis,  which  is  suggested  by 
many  other  features  of  the  Atlantic  shore  line  of  North  America,  that  the 
shore  line  in  later  Paleozoic  time  lay  farther  east  than  it  does  at  present. 

ORIGIIS  AL   DISTRIBUTIOIV  OF  THE   EAST  APPALACHIAjV  COAL   FIELD. 

The  distribution  of  the  Carboniferous  strata  with  reference  to  the  main 
axis  of  the  Appalachian  system  affords  some  valuable  information  as  to  the 
movements  and  attitudes  of  the  continent  during  the  later  stages  of  Paleo- 
zoic and  the  earlier  stages  of  Mesozoic  time.  It  is  noteworthy  that,  while 
the  Carboniferous  of  the  West  Appalachians  extends  to  the  southward 
until  the  beds  pass  beneath  the  Cretaceous  and  Tertiary  deposits  which  lie 
to  the  north  of  the  Gulf  of  Mexico,  rocks  of  that  age  are  wanting  along  the 
Atlantic  coast  until  we  attain  the  latitude  of  northern  Connecticut  and 
southern  Massachusetts.  Thence  to  northern  Newfoundland  accumulations 
of  this  age  occur,  though  in  detached  basins  which  were  evidently  formed 
as  somewhat  separate  areas.  The  uniform  absence  of  Carboniferoits  deposits, 
and  indeed  of  the  Paleozoic  beds  above  the  Silurian  horizon,  along  the 
southern  portion  of  the  Atlantic  coast  line  of  the  United  States,  clearly  indi- 
cates the  long  continuance  of  this  part  of  the  continent  in  the  emerged  state, 
a  state  which  appears  to  have  continued  in  the  southern  section  to  Triassic 
time,  and  perhaps  to  the  Newark  division  of  that  age.  If  Coal  Measures 
strata  had  been  deposited  on  this  part  of  the  Atlantic  coast  above  the  pres- 
ent sea  level,  it  is  hardly  to  be  believed  that  considerable  remnants  would 
not  have  remained  in  the  Dan  River,  Richmond,  and  other  basins.  The 
natural  conclusion  is  that  these  beds  were  not  laid  down,  but  that  the  shore 
from  the  Hudson  southward  remained  in  the  elevated  state,  and  that  in  this 
field  Carboniferous  strata  were  not  accumulated,  while  farther  north  the 
conditions  so  favored  this  work  of  deposition  within  the  region  about  the 
mouth  of  the  St.  Lawrence  that  the  sections  of  this  stratigraphical  division 
are  on  the  average  thicker  than  they  are  in  the  West  Appalachian  field. 

With  the  advent  of  the  Triassic  epoch  the  whole  coast  line  appears  to 
have  been  lowered,  so  that  the  beds  of  this  age  probably  formed  a  more  or 
less  continuous  sheet  from  South  Carolina  to  Nova  Scotia. 

In  the  Carboniferous  downsinking  of  the  eastern  shore  the  conditions 
which  brought  about  the  formation  of  the  Coal  Measures  do  not  seem  to 
have  extended  as  far  south  as  the  valley  of  the  Connecticut.     The  pre- 


ATLANTIC  COAST  BASINS.  39 

sumption  that  this  trough  is  old,  and  that  in  the  Carboniferous  period,  if  it 
had  been  sufficiently  low  lying,  it  would  have  afforded  a  favorable  field 
for  the  accumulation  of  strata,  is  supported  by  the  fact  that  Helderberg 
strata  are  found  within  its  bounds,  and  the  absence  of  the  later  Paleozoic 
is  fair  proof  that  the  trough  was  so  placed  that  it  remained  subjected  to 
erosion.  In  this  connection  it  is  interesting  to  note  that  the  Triassic 
period  does  not  appear  to  have  introduced  true  marine  conditions  along 
this  coast  line.  The  fossils  indicate  that  the  beds  were  formed  either  m 
fresh-water  lakes  or  in  estuaries.  So,  too,  the  Carboniferous  strata  of  the 
East  Appalachian  district  contain  only  fresh-water  fossils,  notably  lacking 
the  thin  beds  containing  marine  fossils  which  in  the  West  Appalachian 
district  clearly  indicate  successive  invasions  of  the  sea.  These  facts  are 
best  explicable  on  the  supposition  that  the  Atlantic  coast  in  this  part  of  its 
history  lay  farther  to  the  east  than  it  does  at  present,  and  that  all  the  beds 
from  the  beginning  of  the  Carboniferous  upward  through  the  greater  por- 
tion of  the  Triassic  section  were  formed  in  basins  so  far  separated  from  the 
sea  that  no  marine  life  found  access  to  them. 

The  development  of  fresh-water  basins  on  the  Atlantic  coast  in  the  Car- 
boniferous period  has  perhaps  its  parallel  on  a  larger  scale  in  that  curious 
formation  of  shallow  lakes  which  occurred  in  Cretaceous  time  along  the 
eastern  border  of  the  Cordillex-as  of  North  America,  and  which  gave  during 
the  Mesozoic  and  a  part  of  Tertiary  time  the  nearly  continuous  fresh-water 
areas  from  Texas  to  the  high  North.  Depressions  of  this  nature  appear  to 
be  of  common  occurrence  along  the  bases  of  mountain  ranges  which  have 
recently  been  subjected  to  extensive  movements.  It  seems  possible,  indeed, 
that  they  are  due  to  counterthrust  action,  which  tends  to  bear  down  the 
part  of  the  earth  immediately  outside  of  the  field  of  considerable  elevation. 
Phenomena  of  this  sort  are  traceable  not  only  in  this  country,  but  around 
the  margin  of  the  Alps  and  other  mountain  districts  which  have  been  suffi- 
ciently well  mapped  to  give  indications  of  these  old  basins.  On  this  suppo- 
sition we  can  account  for  the  general  tendency  of  the  East  Appalachian 
district  to  subside  during  the  time  when  the  neighboring  ranges  were  under- 
going elevation.  The  intensification  of  this  subsidence  at  particular  points 
and  the  conseqiient  infolding  of  strata,  which  have  thus  been  preserved  from 
erosion,  is  to  be  explained  through  the  accumulation  of  thick  deposits  of 
unconsolidated  rocks  in  preexisting  erosion  troughs. 


40  GEOLOGY  OF  THE  NAREAGANSETT  BASIN. 

AIS^CIENT  MARGIN  OF  THE  BASIX. 

The  original  extension  of  the  Carboniferous  beds  the  remains  of 
which  are  found  in  the  Narragansett  Basin  can  not  be  determined.  The 
e^adence  goes  to  show  that  in  the  process  of  filhng  the  trough  the  margin 
of  the  iield  in  which  the  deposits  were  accumulated  extended  in  a  somewliat 
continuous  manner  in  every  direction,  this  extension  being  in  a  way  coin- 
cident with  the  2:)rogressive  subsidence  of  the  area.  There  must  thus  have 
been  a  succession  of  shore  lines,  each  lying  farther  away  from  what  is  now 
the  central  portion  of  the  field.  It  is  probable  that  the  arkose  deposits  which 
are  now  found  around  a  large  part  of  the  margin  of  the  existing  Carbon- 
iferous area  were  accumulated  at  no  great  distance  froni  what  was  the  shore 
line  at  the  time  the}'  were  formed;  but  the  later  shore,  answering  in  age  to 
the  upper  conglomerate,  may  have  been  some  scores  of  miles  beyond  the 
present  limits  of  the  Carboniferous  rocks,  the  materials  being  brought  in 
over  the  shelf  of  earlier-formed  deposits.  The  fact  before  adverted  to,  that 
the  fossil-bearing  quartzite  pebbles  come  from  some  unknown  and  possibly 
rather  remote  district,  indicates  the  validity  of  this  hypothesis. 

Although  the  Carboniferous  section  of  this  basin  is  thick,  the  fact  that 
the  conditions  favored  the  formation  of  rapidly  accumulating  conglomerates 
of  itself  suggests  that  some  portion  of  the  section  has  been  worn  away 
The  fact  that  no  higher-lying  beds  than  the  Carboniferous  exist  in  this  por- 
tion of  New  England,  although  there  is  abundant  evidence  that  a  large 
amount  of  erosion  has  taken  place  since  the  time  of  the  Coal  Measures,  is 
also  evidence  that  a  considerable  thickness  of  stratified  rocks  must  have 
disappeared  from  this  field.  The  margin  of  these  vanished  formations 
must  have  been  far  beyond  the  limits  of  the  Narragansett  Basin. 

RELATIVE  EROSIOK  OF  EAST  A^s^D  WEST  APPAEACHIAlSrS. 

It  requires  but  a  glance  at  the  topography  of  the  districts  l}'ing  to  the 
east  and  to  the  west  of  the  ancient  or  mid-Appalachian  field  to  show 
the  observer  that  there  has  been  a  great  difference  in  their  erosional  history. 
On  the  west  we  find  the  mountain  folds  on  the  whole  well  preserved  as 
regards  both  their  anticlinal  and  their  synclinal  elements,  the  average  pres- 
ervation of  the  structural  features  being  more  perfect  than  that  of  any 
other  equallv  well-known  great  mountains,  except,  it  may  be,  portions  of 


AGE  OF  DISLOCATIONS.  41 

the  Jura.  In  most  cases  the  crests  of  the  anticHnes  have  been  widely 
opened  by  erosive  processes,  and  in  some  rare  instances  the  destruction  has 
advanced  so  far  that  the  synchnal  element  in  the  foldings  has  come  to  lie 
farther  above  the  neighboring  drainag-e  than  the  existing  crests  of  the 
upfolds.  Notwithstanding  this  excessive  local  downweai'ing  which  has  here 
and  there  taken  place,  the  West  Appalachians  have  everywhere,  except  in 
their  extreme  southern  part,  retained  a  striking  topographical  relief.  It  is 
indeed  easy  to  see,  even  in  the  most  ruiiied  part  of  these  great  geological 
edifices,  the  plan  of  the  structure  and  the  g-eneral  features  of  their  archi- 
tecture. It  is  quite  otherwise  with  the  related  elevations  of  the  Atlantic 
coast.  As  before  noted,  the  East  Appalachians  have,  in  their  topographical 
expression,  scarcely  a  semblance  of  the  structure  of  the  West  Appalachians. 
In  fact,  their  lack  of  relief  has  to  this  day  hidden  from  geologists  their  real 
importance  as  orogenic  phenomena. 

Between  Greorgia  and  the  Bay  of  Fundy  none  of  these  mountains  have 
any  distinct  topographical  relief.  Here  and  there  the  crystalline  rock  which 
were  formed  under  their  anticlines,  or  the  massive  outbreaks  of  igneous 
rocks  which  took  place  during  the  folding,  remain  as  considerable  hills,  or 
in  the  case  of  the  Mount  Desert  elevations  the}^  may  attain  the  height  of 
1,000  feet  or  more;  but  in  the  Narragansett  Basin,  although  the  folds  cer- 
tainly have  a  geological  relief  of  not  less  than  10,000  feet,  the  actual  differ- 
ences in  altitude  from  the  depth  of  the  present  water  channels  to  the  highest 
elevations  does  not  exceed  500  feet.  If  these  mountains  of  the  East 
Appalachians  had  been  no  more  worn  down  than  the  Alleghenies,  they 
would  afford  the  most  majestic  elevations  in  the  eastern  part  of  the  continent, 
instead  of  having  no  distinct  value  in  respect  of  topographical  relief 

It  might  at  first  be  supposed  that  the  age  of  these  eastern  reliefs  is 
greater  than  that  of  the  western  dislocations;  the  evidence,  however,  points 
to  the  conclusion  that,  while  some  part  of  the  dislocations  may  be  due  to 
stresses  which  were  of  Cambrian  or  Silurian  age,  the  greater  of  these 
accidents  date  from  post-Carb(niiferous  times,  and  are  probably  to  be 
assigned  to  the  age  of  the  Trias  or  the  Jura.  The  disturbances  which  have 
contorted  the  Cretaceous  or  Tertiary  rocks  of  Marthas  Vineyard  clearly 
indicate  that  the  orogenic  forces  have  acted  along  the  Atlantic  coast  with 
much  energy  down  to  very  modern  time.  To  what,  then,  can  we  attribute 
the  very  great  differences  in  the  relief  of  these  two  mountain-built  districts? 


42  GEOLOGY  OF  THE  XARRAGANSETT  BASHS^. 

The  modern  school  of  topographical  geologists  is  disposed  to  explain 
such  differences  as  those  which  we  are  considering  hj  the  supposition  that 
the  region  of  less  relief — the  eastern — has  been  long  base-leveled,  without 
the  refreshment  of  its  relief  which  is  induced  by  a  subsequent  process  of 
reelevation;  while  the  western  district,  having  been  once,  or  perhaps  more 
than  once,  worn  down  to  near  the  ultimate  erosion  plane,  was  lifted  again 
to  a  height  which  permitted  the  machinery  of  its  torrents  to  sculpture  new 
reliefs.  In  favor  of  this  supposition  there  is  the  fact  that  the  summit  levels 
of  many  peaks  in  the  West  Appalachians  are  so  nearly  in  one  plane  that  it 
is  not  unreasonable  to  suppose,  as  a  working  hypothesis,  that  the  valleys 
have  worn  down  from  an  ancient  base-level.  To  this  suggestion  it  may  be 
answered  that,  so  far  as  the  evidence  goes,  there  is  reason  to  believe  that 
the  eastern  shore  has  shared  in  these  upward  movements.  The  Berkshire 
Hills  shoAv,  by  the  coincident  levels  of  their  summits,  as  distinct  a  trace 
of  base-level  as  do  the  Alleghenies.  Moreover,  in  ,the  immediate  vicinity 
of  the  Narragansett  Basin  the  broad  ridges  of  the  Worcester  axis  carry  its 
levels  to  about  1,000  feet.  Yet  it  is  plain  that  this  set  of  folds  owes  its 
origin  to  the  same  movements  that  developed  those  of  the  Bay  district.  In 
a  word,  even  if  we  allow  that  uplift  after  base-leveling  in  the  one  case  and 
lack  of  the  upward  movement  in  the  other  might  account  for  the  very  great 
difference  in  conditions,  we  have  not  the  means  to  verify  the  hypothesis;  it 
therefore  has  no  apparent  value  to  us  in  interpreting  this  field. 

Although  I  regard  the  considerations  which  are  commonly  included 
under  the  title  of  "base-leveling"  as  one  of  the  most  important  conti'ibutions 
to  physiographical  geology,  it  seems  to  me  that  we  must  guard  against  the 
danger  of  inferring  too  much  concerning  the  existence  of  ancient  leveling 
of  the  land  down  to  near  the  plane  of  the  sea  from  the  seeming-  accords  in 
the  altitudes  of  mountain  summits.  It  is  easy  to  see  that  this  accord  is  only 
of  a  very  general  nature,  it  being  necessary  in  the  classification  to  allow  a 
range  of  elevation  amounting  to  several  hundred  feet.  It  may  well  be  that, 
beginning  with  the  utmost  diversity  which  could  have  existed  in  the  heights 
of  the  Alleghenies,  the  pi'ocess  of  downwearing  might  have  bi'ought  about 
as  near  an  approach  to  uniformity  of  height  as  actually  exists  in  the  peaks 
of  that  range.  So  long  as  the  rocks  are  of  like  hardness  and  the  folds  of 
like  size,  the  tendency  would  be  to  keep  the  downwearing  crests  at  some- 
where near  the  same  level. 


CONTINENTAL  SHELF.  43 

Another  reason  for  the  disappearance  of  the  topographical  rehef  of  the 
East  Appalachians  can  be  found  in  the  marine  erosion  to  which  they  have 
been  subjected.  As  before  remarked,  it  is  evident  that  the  Atlantic  coast  of 
this  continent  has  for  a  very  long  time  been  in  about  its  present  relations 
to  the  sea.  It  is  characteristically  an  old  shore,  and  has  the  marks  of  age 
in  the  broad  continental  shelf  which  fringes  it  on  the  east  and  in  the  wide 
belt  of  lowlands  which  lies  to  the  landward  of  the  coast  line.  These  two 
features  seem  to  be  closely  related  to  each  other;  the  submarine  shelf 
probably  represents  in  good  part  the  accumulations  of  d(ibris  which  has 
been  worn  from  the  bench  which  the  sea  has  cut  into  the. land. 

Because  it  is  covered  by  the  sea,  w^e  can  determine  but  little  of  the 
continental  shelf,  except  by  inference  from  what  we  reasonablv  take  to  be 
an  emerged  part  of  its  mass  as  it  appears  in  the  structure  of  the  great 
southern  coastal  plain,  that  plain  land  being  evidently  composed  of  conti- 
nental waste  in  part  removed  by  marine  action,  together  with  the  ddbris  of 
organic  forms;  biit  of  the  bench  we  may  know  much,  for  the  greater  part 
of  it  is  above  the  sea  level.  If  the  student  would  appreciate  the  importance 
of  this  seaboard  bench  on  the  Atlantic  coast  of  the  United  States,  he  should 
study  the  section  from  the  great  Appalachian  Valley  to  the  sea.  Probably 
the  most  instructive  section  is  from  the  region  of  the  upper  Shenandoah  to 
the  region  about  Fort  Monroe,  in  Virginia.  It  is  readily  noted  that  the 
crystalline  rocks  on  the  western  side  of  the  Blue  Ridge  rise  steeply 
from  the  broad  vale  which  is  occupied  by  the  Cambrian  beds.  On  this 
side  of  the  ridge  there  is  no  trace  of  benching ;  the  mountain  sides  show  the 
ordinary  torrent  slopes.  On  the  eastern  side  of  the  ridge,  however,  there 
lies  the  extensive  rolling  country  commonly  known  as  the  "Piedmont 
Plateau,"  which  has  been  recognized  as  a  jjeculiar  feature  in  the  section 
from  New  Jersey  to  Georgia  ever  since  the  country  was  occupied  by  the 
Europeans.  This  region  has  peculiarities  of  soil  and  of  surface  aspect 
which  are  due  to  the  fact  that  it  is  to  a  great  extent  underlain  by  crystalline 
or  metamorphosed  rocks  essentially  like  the  complex  which  makes  the 
higher  country  of  the  Blue  Ridge.  When  the  rocks  exhibit  bedding,  the 
attitudes  of  the  strata  indicate  highly  compressed  mountain  folds.  The 
topography  of  the  district  shows  much  torrent  cutting  on  the  surface  of  a 
sloping  bench  which  declined  toward  the  sea  at  the  rate  of  10  or  20  feet 
to  the  mile,  the  upper  or  northern  margin  of  this  bench  passing  rather 
suddenly  into  the  steep  slopes  of  the  mountain  ranges. 


44  GEOLOGY  OF  THE  ISTAERAGAIN^SETT  BASIX. 

The  coiiditioDS  of  the  surface  are  in  the  main  as  shown  in  PL  I,  with 
the  exception  that  occasional  outliers  of  high  land  are  found  over  the 
Piedmont  district.  These  outliers  have  the  g-eneral  aspect  of  ancient 
islands,  the  bases  of  which  have  of  late  been  elevated  above  the  sea 
level. 

Perhaps  the  best  instance  of  these  structures  is  afforded  by  King- 
Mountain,  North  Carolina,  which,  as  has  recently  been  sll0^vn  hj  the  studies 
of  Prof  Collier  Cobb,  of  the  University  of  North  Carolina,  is  an  insular 
mass  which  has  by  elevation  been  embodied  in  the  area  of  the  emerged 
continent. 

It  should  be  said  that  this  bench,  with  local  variations,  extends  along 
the  Atlantic  coast  of  the  continent  as  far  north  as  the  St.  Lawrence  district, 
but  that  the  ancient  islands  are  nowhere  so  well  shown  as  in  the  Cai-oliuian 
section. 

The  foregoing  statements  will  make  plain  the  working  hypothesis  as 
to  the  erosion  of  the  East  Appalachian  reliefs.  We  see  that  these  moun- 
tains lie  in  the  realm  of  the  marine  bench,  that  border  land  of  the  continent, 
where  the  repeated  up  and  down  goings  of  the  sea  bring  the  machinery  of 
the  surf  and  the  other  erosive  agents  of  the  coast  line — the  frost,  the  tides, 
and  the  winds — to  bear  in  succession  on  every  part  of  the  surface.  In 
recent  years  there  has  been  a  disposition  to  deny  to  marine  action  any 
considerable  effect  on  the  topography  of  a  country.  This  limited  view 
is  a  natural  recoil  from  the  old  notion  that  the  sea  is  the  principal  agent 
in  land  carving.  From  overestimating  the  value  of  a  natural  agent,  the 
inevitable  step  is  toward  an  underreckoning,  which  seems  in  this  case  to 
have  gone  altogether  too  far.  A  part  of  the  misestimation  as  to  the  ero- 
sional  value  of  tlie  shore  agents  is  due  to  the  study  of  coastal  processes  in 
what  we  may  term  adjusted  shore  lines,  such  as  are  to  be  found  where  the 
sea  has  acted  for  a  long-  time  on  a  coast  where  the  lands  have  not  altered 
in  their  position  with  reference  to  the  sea.  In  such  conditions  the  sea,  by 
a  complicated  system  of  actions,  builds  a  series  of  obstructions  in  the  way 
of  shallows  and  beaches,  which  serve  to  bar  the  land  from  its  assault,  and 
which  often  cause  the  energy  of  the  waves  and  tide  to  be  expended  in  such 
wise  as  little  if  at  all  to  erode  the  laud.  Wherever  we  are  able  to  study  the 
action  of  the  sea  where  the  land  is  rapidly  oscillating,  we  note  at  once  the 
great  increase  in  the  effectiveness  of  the  ocean's  work.     Thus,  on  the  coast  of 


EFFECTS  OF  CHANGES  OF  LEVEL.  45 

New  Jersey,  where  the  subsidence  is  at  the  rate  of  perhaps  2  feet  in  a  cen- 
tury, the  formation  of  the  usual  sand  barrier  beaches  is  prevented  for  a 
considerable  section,  with  the  result  that  the  sea,  save  for  the  interference 
of  man,  works  back  into  the  cliffs  at  the  rate  of  several  feet  in  a  5^ear. 

While  a  process  of  subsidence  is  in  general  favorable  to  marine  erosion, 
that  of  elevation  is  probably  yet  more  advantageous  to  the  wave  and  cur- 
rent work;  and  this  for  the  following  reasons.  When  the  land  sinks,  the 
debris  due  to  the  surf  remains  in  the  possession  of  the  sea  and  may  be 
used  to  build  barrier  beaches  at  a  higher  level.  Off  the  coast  of  North 
Carolina,  where  there  is  also  a  subsidence  movement,  because  the  amoiuit 
of  sand  is  large,  the  beaches  are  still  effective  walls  against  the  sea. 
When  the  land  rises,  however,  the  beach  material  is  constantly  left  behind 
in  the  elevated  coast  lines,  and  at  each  successive  zone  of  attack  the  sea 
assails  an  unmasked  shore.  At  present  we  appear  to  be  in  a  period  where 
the  land  oscillations  are  relatively  very  slight;  we  therefore  are  in  a  posi- 
tion where  we  would  naturally  underestimate  the  true  measure  of  marine 
erosion.  Still,  taken  in  a  large  way,  we  can  easily  see  that  the  coastal 
erosion  is  by  far  the  most  effective  at  the  times,  which  we  know  to  be  fre- 
quent, when  the  shore  is  moving  upward  or  downward.  This  shoreward- 
sloping  bench  may  be  taken  as  the  result  of  the  two  main  varieties  of  land 
Avearing— that  due  to  the  natural  work  of  the  rainfall,  and  that  due  mainh"  to 
the  sti-oke  of  the  waves  as  they  break  upon  the  coast.  In  the  equation  which 
determines  the  slope  of  the  coastal  bench,  we  have  to  reckon  the  effect 
of  many  agents  and  conditions.  Among  these,  the  successive  changes  of 
the  base-level— i.  e.,  the  plane  of  the  sea — are  obviously  of  great  importance. 
As  the  surface  of  the  bench  gains  in  height,  the  capacity  of  the  marine 
agents  become  relatively  diminished,  for  the  reason  that  the  marine  cliff 
grows  higher  and  the  waves  have  more  deportation  to  effect  for  each  unit 
of  the  extension  of  the  scarf  into  the  land.  On  the  other  hand,  with  the 
gain  in  height  there  comes  a  proportional  gain  in  the  wearing  power  of  the 
rain  water,  the  capacity  of  which  to  do  wearing  work  is  directly  rehxted  to 
the  height  above  the  sea  at  which  it  comes  upon  the  land. 

Although  the  conditions  which  are  no\v  found  on  the  Atlantic  coast  of 
the  countr}^  are  clearly  less  favorable  to  erosion  than  the  average,  it  is  evi- 
dent to  the  attentive  observer  that  the  amount  of  marine  erosion  which  is 
now    done    along   the   coast  from   Cape  Hatteras  to  Canada    equals   if  it 


46  GEOLOGY  OF  THE  NAREAGANSETT  BASIK 

does  not  exceed  in  volume  that  which  is  accomplished  by  all  the  rivers 
which  empty  into  the  sea  along  this  part  of  the  shore.  We  may  say,  indeed, 
that  the  evidence,  when  fairly  considered,  leads  ns  to  the  conclusion  that 
the  destruction  of  the  reliefs  in  the  Atlantic  coast  mountains — the  East 
Appalachians,  as  we  have  termed  them — has  been  in  a  large  measure  due 
to  the  long-continued  action  of  the  sea  on  the  zone  in  which  they  lie. 

In  the  case  of  the  Narragansett  Basin  it  seems  impossible  to  account 
for  the  destruction  of  the  original  reliefs  by  the  action  of  water  on  its  way 
to  the  sea.  If  we  take  account  of  the  existing  water-filled  troughs,  the  arms 
of  the  sea,  and  the  rivers,  we  find  a  plain  cut  by  relatively  wide  and  shal- 
low canyons,  which  are  now  to  a  great  extent  filled  with  drift.  This  plain 
is  underlain  by  rocks  of  very  diverse  hardness,  so  that  if  its  surface  were 
due  to  the  result  of  the  downwearing  action  of  streams  it  should  he  most 
irregularly  carved,  in  place  of  having  that  shorn-off'  aspect  which  the 
horizontally  delivered  stroke  of  the  waves  produces.  Therefore  we  may 
conclude  that  the  difference  between  the  reliefs  of  the  East  and  the  West 
Appalachians  requires  us  to  consider  the  benching'  action  of  the  sea  along- with 
the  base-leveling  process  effected  by  rivers.  Undoubtedly  this  latter  base- 
leveling  action  has  to  be  reckoned,  but  only  as  one,  possibly  the  least, 
important  element  in  the  action.  It  may  be  noted,  in  order  to  complete 
this  interesting  storv,  that  the  greater  part  of  the  West  Appalachians  Avas 
fully  protected  ag'ainst  the  action  of  the  Atlantic  by  the  rampart  of  the 
Blue  Ridge.  It  is  a  .corroboration  of  the  h}"pothesis  that  at  the  southern 
end  of  the  A¥est  Appalachians,  where  these  mountains  were  exposed  to  the 
action  of  the  waves  of  the  Gulf  of  Mexico  probably  at  least  until  the  end 
of  the  Cretaceous  or  the  middle  of  the  Tertiary  period,  the  mountains  show 
a  measure  of  erosive  action  hardly  less  than  that  which  is  exhibited  by  the 
worn-down  ridges  of  the  Atlantic  seaboard 

Some  further  considei'ation  of  the  question  as  to  the  wearing  down  of 
the  rocks  of  this  basin  will  be  found  in  the  next  chapter,  on  the  glacial 
history  of  the  field. 

RECENT  CHAXGES  OF  LEVEL. 

It  may  be  well  in  this  connection  to  note  the  facts  concerning'  the 
recent  changes  of  level  in  the  Narragansett  Basin.  As  elsewhere  remarked, 
the  evidence  goes  to  sIioaa'  that  the  amount  oi  glacial  wearing,  or  at  least 


EFFECTS  OF  WAVE  ACTION.  47 

that  of  the  last  ice  epoch,  on  this  field  was  limited.  We  may  therefore 
assume,  what  is  inferred  from  other  evidence,  that  the  drainage  of  the 
district  is  substantially  the  same  as  it  was  before  the  last  ad^'ent  of  the 
glaciers.  The  drainage  consists  of  sundry  deep  channels,  the  arms  of 
Narragansett  Bay  and  their  continuations  in  the  narrowed  rivers.  To 
explain  these  stream  beds,  we  must  assume  that  the  surface  of  the  country 
was  considerably  higher  during  the  preglacial  time  than  it  is  at  the  present 
day.  If,  as  is  probably  the  case,  the  central  part  of  the  bottom  of  Nar- 
ragansett Bay  is  filled  in  with  mud  to  the  depth  of  100  feet  or  more,  as  is 
the  case  with  other  channels  of  like  character  on  this  part  of  the  coast, 
theu  the  recent  subsidence  may  exceed  300  feet.  A  like  process  of  reason- 
ing applied  to  other  parts  of  the  shore  between  the  Delaware  and  tlie  St. 
Lawrence  leads  to  approximately  the  same  conclusion  as  to  the  amount  in 
which  the  sea  has  gained  on  the  land.  It  should  be  said,  however,  that  this 
change  in  the  position  of  the  shore  may  be  due  to  an  alteration  in  the  level 
of  the  sea  itself  quite  as  well  as  to  the  lowering  of  the  land  in  this  jjart  ol 
the  shore;  in  fact,  the  extent  of  this  modern  invasion  of  the  land  by  the 
sea  along  nearly  all  the  shores  of  the  continents  raises  the  presumi^tion  that 
the  action  may  have  been  due  to  a  vast  movement  of  the  floor  in  some  part 
of  the  ocean  realm. 

GEXERAt,   STATEMEXT   COXCERXHSTG  BASE-LEVELIKG. 

What  has  Ijeen  said  in  the  preceding  pages  concerning  the  relations  of 
marine  and  laud  denudation  makes  it  desirable  to  assemble  the  considerations 
which  bear  upon  this  problem. 

There  can  be  no  question  as  to  the  importance  of  the  base-leveling- 
theory,  which  assigns  to  the  atmospheric  agents  of  erosion  the  downwearing 
of  the  land  masses.  It  should  be  noted,  however,  that  the  marine  agents — 
the  cutting  action  of  tlie  waves  and  the  marine  currents  dependent  on  wind 
and  tidal  work — have  in  their  appropriate  place  a  certain  amount  of  influ- 
ence. It  should  also  be  noted  that  as  the  land  is  worn  down  toward  the 
level  of  the  sea  the  efficiency  of  the  atmospheric  forces  in  the  work  of 
further  reduction  continually  diminishes,  because  of  the  lessened  fall  of  the 
streams  and  from  the  tendency  of  the  surface  to  become  deeply  covered 
with  a  protecting  detrital  envelope. 

In  the  low  levels  of  the  land,  where  the  aerial  ao-ents  become  less 


48  GEOLOGY  OF  THE  NAREAGANSETT  BASIN. 

effective,  we  may  always  expect  to  find  some  effect  arising  from  the  repeated 
visitations  of  the  sea  brought  about  by  the  ahnost  continual  oscillations  in  ' 
the  height  of  tlie  land.  The  measure  of  this  marine  work  is  commonly  the 
greater  the  nearer  we  attain  to  the  average  level  about  which  the  sea  has 
oscillated  for  a  considerable  time.  Thus  marine  action  comes  in  to  sup- 
plement that  of  the  atmosphere. 

Along  the  coast  of  New  England,  and  particularly  in  the  district  con- 
sidered in  this  report,  within  the  limits  of  the  recent  oscillations  of  marine 
level,  we  find  at  man}'-  points  evidence  that  the  sea  at  higher  stations  than 
now  worked  to  remove  the  coating  of  detritus  and  to  expose  large  areas 
of  the  surface  to  the  process  of  decay,  which  rapidly  tends  to  break  up  the 
rocks.  This  part  of  the  marine  work,  in  favoring  erosion,  is  perhaps  of  as 
much  consequence  as  that  due  to  the  direct  cutting  action  of  the  sea. 

It  may  be  remarked  that  the  frequent  invasions  of  the  sea,  by  producing 
plains  of  detrital  material,  such  as  those  which  exist  in  the  southern  part  of 
the  United  States,  tend  also  to  reduce  the  surface  of  the  land  to  an 
approximately  level  form.  Thus  the  evidence  goes  to  show  that  beneath 
the  southern  plain  the  contour  of  the  ancient  rocks  is  irregular,  they  having 
been  mantled  over  by  a  thick  coating  of  debris  accumulated  along  the 
continental  shelf  We  therefore  see  that  the  ocean  tends  in  two  diverse 
ways  to  bring  about  coastal  plains — first,  by  aiding  in  wearing  down  origi- 
nally irregular  surfaces  to  a  level  attitude;  and  secondly,  by  constructing 
detrital  plains  over  those  surfaces  winch  in  part  have  thus  been  brought  to 
a  nearly  horizontal  attitude. 

As  for  the  oscillations  of  the  land  which  serve  to  bring  the  mill  of  the 
surf  at  various  levels  over  its  surface,  it  may  be  said  that  since  the  Carbon- 
iferous period  tiiere  is  evidence  of  many  such  swingings,  which  have  brought 
the  plane  of  the  sea  from  a  few  score  to  several  hundred  feet  above  its 
present  position  on  the  Atlantic  base  of  the  continent.  The  evidence  to 
the  same  effect  from  other  regions  is  so  extensive  that  it  may  be  called  a 
world-Avide  phenomenon.  It  may  safely  be  assumed  that  coast  lines  are 
normall}^  instable,  and  this  through  a  range  of  several  hundred  feet. 

As  to  the  amount  of  cutting  which  can  be  effected  by  the  sea  in  pro- 
portion to  that  which  may  be  accomplished  by  the  descent  of  waters  from 
a  high  level  to  the  shore  line,  the  facts  are  not  yet  sufficiently  ascertained 
to  permit  any  definite  statement.  It  may  be  said,  however,  that  where  the 
exposure  is  such  that  the  waves  may  assault  the  shore  with  considerable 


SUCCESSIONS  OF  DEPOSITION,  49 

energy,  especially  where  the  tides  are  high,  the  erosion,  even  in  a  brief  period 
of  geological  time,  is  often  very  great.  Thus  on  the  coast  of  Yorkshire,  north 
and  south  of  Whitby,  the  marine  clitfs,  apparently  formed  in  the  brief 
period  during  which  the  sea  along  that  coast  has  had  its  present  attitude, 
have  an  average  height  of  several  hundred  feet,  and  the  platform  which 
marks  the  lower  range  of  wave  action  extends  on  the  average  a  mile  or 
more  from  the  shore.  The  prism  of  rock  removed  by  this  cutting  is  in 
mass  greater  than  we  can  well  assume  to  have  been  eroded  from  the  land  dur- 
ing the  same  period  for  the  distance  of  20  or  30  miles  from  the  coast  line. 
Along  the  shore  of  New  England,  though  the  coast  generally  lies  against 
rocks  of  more  than  usual  hardness,  the  benching  action  of  the  sea  is  almost 
always  noticeable.  In  the  few  thousand  years  during  which  this  coast  line 
has  remained  at  its  present  attitude,  the  amount  of  erosion  has  apparently 
been  many  times  as  great  as  over  any  equally  extensive  interior  portion  of 
the  field  subject  to  the  action  of  atmospheric  agents.  Considering  only  the 
hard  rocks,  especially  those  of  the  coast  of  Maine,  I  am  of  the  opinion  that 
the  atmospheric  erosion  accomplished  in  New  England  since  the  Glacial 
period  has  not  been  so  great  as  that  effected  along  the  shore  belt  in  the 
much  shorter  time  which  has  elapsed  since  those  coasts  began  to  be  assaulted 
by  the  sea. 

It  is  to  be  observed  that,  in  all  estimates  as  to  the  relative  value  of 
marine  and  atmospheric  erosion,  account  must  be  taken  of  the  dissolving 
action  of  the  land  waters,  which  is  always  wanting  in  the  case  of  the  sea. 
Although  the  interior  erosion  of  New  England  is  now  exceedingly  small, 
the  solutional  decay  is  gradually,  indeed  it  may  be  said  somewhat  rapidly, 
advancing  in  certain  portions  of  the  glacial  deposits,  so  that  the  time  will 
come  when  they  may  pass  off  with  greater  rapidity.  Making  allowance  for 
this  and  for  other  evident  qualifications  as  to  the  relative  value  of  marine 
and  interior  erosion,  it  may  still  be  said  that  the  former  agent  has  a  certain 
and  important,  though  much  neglected,  influence  in  determining  the  shape 
of  the  lower-lying  portions  of  the  land  mass. 

CYCliES  OF  DEPOSITIOI^. 

Considerations  as  to  the  succession  of  phenomena  of  deposition  which 
were  brought  into  view  by  the  writings  of  the  late  Prof  John  S.  Newberry 
and  others,  appear  to  receive  no  support  from  the  successions  of  strata  in 
HON  xxxiir 4 


50  GEOLOGY  OF  THE  NARRAGANSETT  BASIN. 

the  Narragansett  Basiii.  The  first  stage  of  deposition  in  this  field,  when 
the  formation  of  the  Carboniferous  section  began,  is  marked  by  the  occur- 
rence of  fragmental  beds,  mainly  arkoses.  Where  the  succession  is  well 
displayed,  these  arkoses  are  followed  by  conglomerates  of  no  great  magni- 
tude. Succeeding  these  with  tolerable  uniformity  comes  a  section  of  several 
thousand  feet  where  the  deposits  are  prevailingly  rather  fine  grained.  In 
the  ujDper  half  of  the  section  there  is  a  return  to  conglomerate-making- 
conditions.     This  return  appears  to  have  been  made  rather  suddenly. 

At  fii'st  sight  it  seems  reasonable  to  suppose  that  the  succession  of 
events,  as  indicated  in  a  general  way  by  the  section,  gave  (1)  a  period  in 
which  the  shore  line  was  everywhere  near  to  the  margin  of  the  present 
basin,  permitting  the  formation  of  arkose;  (2)  a  period  when  a  continued 
depression  kept  the  shore  line  always  at  a  distance,  resulting  in  the  fine- 
grained beds;  and  (3)  a  reelevation,  which,  by  pushing  the  shores  toward 
the  center  of  the  field,  led  to  the  ready  importation  of  coarse  debris.  It  is 
evident  that  there  are  many  circumstances  which  serve  to  qualify  the 
interpretation  which  can  be  made  as  to  this  and  other  cycles  of  deposition. 
Manifestly  the  intensity  of  erosion,  as  well  as  of  the  transportation  of  detritus 
worn  from  the  land,  depends  in  large  measure  upon  the  ratio  of  the  rainfall 
at  different  times.  As  this  ratio  doubtless  varies  in  different  periods,  or 
even  in  different  parts  of  the  same  period,  the  effect  may  be  to  produce 
great  alterations  in  the  character  of  sediments  brought  to  any  particular  field. 
Moreover,  along  the  coast  line,  when  it  is  in  a  static  condition,  there  is  an 
obvious  tendency  to  produce  a  shelf,  which,  advancing  from  the  shores  of 
the  basin,  may  afford  a  slope  over  which,  in  time,  coarse  sediments  may  be 
transported  to  a  distance  from  the  shore  to  which  they  could  not  at  first 
have  attained.  On  these  and  other  accounts  it  does  not  seem  profitable 
to  attempt  any  conclusions  based  upon  the  succession  of  beds  in  this  area. 

ARKOSE   DEPOSITS   OP  THE   BASIK. 

As  the  interpretation  of  much  of  the  history  of  the  Narragansett  Basin 
depends  on  the  view  that  is  taken  of  the  arkose  dej^osits  which  abundantly 
occur  at  various  points  around  its  margin,  and  are,  indeed,  a  characteristic 
feature  of  that  rim,  it  will  be  necessary  to  consider  the  significance  of  these 
accumulations. 

Geologists  who  have  had  to  deal  with  arkose  deposits  have  generally 
accepted  the  conclusion  that  they  indicate  the  accumulation   of  detrital 


FORMATION  OF  ARKOSES.  51 

materials  derived  from  crystalline  rocks  which  have  been  subjected  to  much 
decay  in  place,  so  that  they  lost  their  original  cohesion  before  they  were 
subjected  to  transportation  and  were  accumulated  in  their  present  situations. 
The  essential  characteristic  of  such  deposits  is  that  they  contain  considerable 
quantities  of  crystalline  materials  in  which  the  fragments  have  not  been 
reduced  to  sand,  but  retain,  in  good  part  at  least,  their  original  form.  In 
other  words,  the  presence  of  arkose  beds  means  an  antecedent  decay  in 
crystalline  rocks,  a  decay  taking  place  in  such  a  manner  as  to  loosen  the 
crystals  from  their  attachments  without  going  far  enough  to  disintegrate 
the  bits.  This  action  has  been  followed  by  the  wearing  away  of  the 
softened  mass  and  the  more  or  less  complete  rearrangement  of  the 
materials. 

In  the  present  state  of  the  study  of  arkose  beds,  pains  has  not  been 
taken  to  discriminate  the  materials  into  the  two  groups  into  which  they  may 
naturally  be  divided.  In  certain  cases,  after  the  process  of  decay  has 
broken  up  the  texture  of  the  crystalline  rock,  and  perhaps  removed  much 
of  its  materials  in  the  state  of  solution,  the  deposit  remains  essentially  in 
its  original  place,  where  it  may  be  covered  by  subsequently  accumulated 
deposits.  Even  though  recementation  of  the  crystals  takes  place,  the 
accumulation  will  have  more  or  less  of  the  character  to  which  we  gave  the 
name  of  arkose.  For  convenience,  we  may  class  this  group  as  unremoved 
arkose. 

Although  the  conditions  which  favor  the  formation  of  unremoved 
arkoses  must  be  of  infrequent  occurrence,  instances  of  the  kind  are  to  be 
observed  in  certain  parts  of  New  England,  where  the  preglacial  decay 
reduced  considerable  quantities  of  the  crystalline  rocks  to  a  disintegrated 
state,  and  where  the  beds  thus  softened  were  not  removed  by  the  glacial 
wearing,  but  remain  to  the  present  day  covered  by  sheets  of  stratified  or 
unstratified  drift.  The  normal  or  transported  arkoses  can,  in  all  cases,  be 
discriminated  from  those  which  have  remained  in  place,  by  the  evidences  of 
water  action  afforded  by  more  or  less  obvious  stratification. 

The  most  characteristic  and  readily  interpretable  deposits  of  arkose 
exhibited  within  the  limits  of  the  Narragansett  Basin,  indeed  one  of  the 
most  important  accumulations  of  this  nature  ever  described,  occurs  at  Steep 
Brook,  the  station  just  north  of  Fall  River,  Massachusetts.  At  this  point, 
lying  against  the  granitic  rocks  which  form  the  western  margin  of  the  basin, 


52  GEOLOGY  OF  THE  NARRAGANSETT  BASIN. 

is  a  section  of  what  at  first  sight  appears  to  be  a  mass  of  granite  which  has 
decayed  in  place.  This  seemed  to  be  the  view  which  was  enforced  by  the 
observed  facts  when  these  beds  were  first  seen  by  me,  about  twenty -five 
years  ago,  and  they  had  just  been  opened  by  prospectors  who  were  led  by 
a  small  outcrop  on  the  brook  to  seek  for  fire  clays.  Further  exploration, 
however,  soon  disclosed  the  fact  that  the  mass  exhibited  traces  of  stratifica- 
tion such  as  were  not  to  be  found  in  the  neighboring  unchanged  granite.  A 
close  study  of  the  obscure  divisional  plane  brought  to  light  the  existence 
in  them  of  many  well-preserved  specimens  of  plants  which  belong  to  the 
Carboniferous  time.  This  evidence  indicates  that  the  deposit  was  formed 
during  the  period  of  the  Coal  Measures.  The  considerable  thickness  of  this 
section  makes  it  clear  that  the  conditions  which  led  to  its  formation  continued 
■  for  a  long  time.  These  conditions  were  substantially  as  follows:  There  was  a 
rapid  importation  of  semidecayed  granitic  rock,  such  as  Avould  be  afforded  by 
the  decomposition  of  the  crystalline  materials  which  are  to  be  fouiad  immedi- 
ately to  the  east  of  the  locality.  The  rateof  this  accumulation  appears  to  have 
been  so  speedy  that  there  was  no  chance  for  a  true  soil  layer  to  be  formed 
on  the  growing  beds.  The  plant  remains  which  occur  were  evidently  not 
grown  on  the  sites  they  now  occupy,  but  were  fragments  swept  into  their 
positions  from  a  distance.  It  appears  likely  that  they  had  been  to  a  greater 
or  less  degree  inclosed  in  ordinary  ferruginous  concretions  before  this 
transportation. 

The  interpretation  of  the  conditions  at  Steep  Brook  during  the  time 
when  the  forces  which  led  to  the  deposition  of  the  arkose  were  in  action 
seems,  in  a  general  way  at  least,  to  be  not  at  all  difficult.  It  is  evident 
that  in  the  time  preceding  the  deposition  of  the  portion  of  the  Carboniferous 
strata  on  which  the  arkoses  lie,  the  portion  of  the  continent  about  the  Narra- 
gansett  Basin  had  been  long  exposed  to  atmospheric  decay  without  having 
been  subjected  to  the  conditions  which  would  remove  the  decomposed 
material  as  rapidly  as  it  was  brought  into  the  disintegrated  form.  Judging 
by  the  conditions  which  have  affected  the  fields  that  now  afford  or  that 
might  produce  the  arkose  deposits,  we  may  assume  tha,t  these  levels  of  the 
Coal  Measures  time  had  long  been  the  seat  of  a  considei'able  rainfall  and 
had  maintained  a  coating  of  vegetation,  such  being  the  antecedent  condi- 
tions of  any  decomposition  which  would  prepare  the  way  for  arkoses. 
After  the  development  of  a  sufficient  depth  of  this  rock  decay,  we  have  to 


DISTRIBUTION  OF  AEKOSES.  53 

suppose  that  conditions  favoring  the  rapid  erosion  of  the  decayed  material 
were  estabhshed.  These  conditions  may  have  been  brought  about  in  any 
one  of  several  ways:  The  region  may  have  been  subjected  to  glacial  action; 
the  rainfall  of  the  area  may  have  been  increased  in  such  a  measure  that  the 
streams  were  made  competent  to  waste  the  surface;  or  the  area  may  have 
been  exposed  to  wave  action,  either  by  being  lowered  beneath  the  level  of 
the  sea  or  by  becoming-  the  seat  of  a  lake. 

The  hypothesis  of  glacial  action  at  the  time  these  arkoses  were  formed 
does  not,  at  first  sight,  seem  to  be  supported  by  the  evidence  which  is  derived 
from  the  presence  of  well-preserved  vegetable  remains  in  the  beds;  but,  as 
remarked  in  the  preceding  paragraph,  these  remains  seem  not  to  have  been 
deposited  in  a,  fresh  state  in  the  growing  accumulation,  but  to  have  been 
washed  from  some  antecedently  formed  but  practically  contemporaneous 
deposit  into  the  positions  which  they  now  occupy.  Therefore  the  existence 
of  ice  wearing  in  this  district  at  the  arkose-building'  time  does  not  seem 
improbable.  We  shall  hereafter  note  that  there  is  other  evidence  of  a  more 
positive  nature  going  to  show  the  existence  of  glacial  conditions  in  this 
gravel  period  in  the  district  a,bout  the  Narragansett  Basin. 

As  a  whole,  the  distribution  of  the  arkose  deposits  of  the  Carboniferous 
time  around  the  margins  of  the  Narragansett  Basin  seems  most  easily  to 
be  explained  by  the  supposition  that  streams  of  a  swiftly  flowing  nature 
formed  torrent  cones  when  they  debouched  into  a  fresh-water  lake  which 
occupied  almost  the  whole  area  now  covered  by  the  coal-bearing  rocks  of 
the  district.  That  the  deposits  are  in  general  those  of  torrent  cones  or 
deltas  appears  to  be  shown  by  their  irregular  distribution.  In  all  cases 
where  they  have  been  observed  they  occur  in  rather  detached  patches,  like 
accumulations  which  have  no  great  extension  in  the  direction  of  the  ancient 
shore  line.  This  seems  to  exclude  the  supposition  that  the  deposits  were 
formed  in  the  manner  of  ordinary  shore  accumulations,  where  the  debris 
is  transported  from  a  neighboring  coast  escarpment. 

There  are  no  observations  on  record  concerning  arkoses  now  in  process 
of  formation,  thoug'h  such  may  be  accumulating  in  many  parts  of  the  world. 
It  is  therefore  not  possible  to  ascertain  with  certainty  the  distance  to 
which  the  angular  crystalline  debris  of  granitic  rocks  can  be  conveyed  by 
stream  action  without  losing  the  peculiar  features  which  separate  it  from 
the  ordinary  products  of  the   erosive  forces  ^^'hich  have  acted  on  much 


54  GEOLOGY  OF  THE  XAERAGAiS'SETT  BASIN. 

decayed  rocks.  It  happens  that  on  the  island  of  Marthas  Vineyard  there 
are  extensive  deposits  of  arkose  formed  during  the  Tertiary  period,  which 
appears  to  indicate  that  materials  of  this  nature  may  be  transported  for 
considerable  distances.  The  deposits  at  Gay  Head  contain  very  thick  beds 
of  arkose,  probably  brought  from  the  granitic  area  lying  to  the  northwest 
of  the  locality.  It  is  difficult  to  conceive  that  the  supply  of  the  detritus 
could  have  been  brought  from  less  than  two  score  miles  away  from  the 
locality  in  question.  It  is  of  course  possible  that  these  Tertiary  arkoses 
were  derived  from  some  granitic  area  near  the  place  where  they  lie — an  area 
which  by  local  subsidence  or  excessive  erosion  has  in  modern  times  been 
brought  below  the  level  of  the  sea;  but  the  evidence  in  these  cases  is  clearly 
against  this  hypothesis  and  in  favor  of  the  assumption  that  the  little-rounded 
crystals  from  the  granitic  sources  have  been  conveyed  for  forty  or  more 
miles.  Therefore,  while  the  Carboniferous  arkoses  afford  clear  evidence 
that  they  were  deposited  along  the  shores  of  a  basin,  no  very  clear  evidence 
as  to  the  field  of  their  derivation  can  be  obtained  from  the  conditions  of 
the  beds. 

The  arkose  deposits  of  the  Narragansett  Basin  are  found  in  both 
groups  of  deposits  which  have  been  observed  in  the  field,  the  Cambrian 
and  the  Carboniferous.  In  the  former  the  evidence  is  limited  to  the  region 
about  Attleboro,  that  being  the  only  portion  of  the  basin  where  the  Cam- 
brian strata  are  clearly  recognizable.  The  Carboniferous  arkoses  are  much 
more  extensively  distributed.  They  may  indeed  be  said  to  occur  as  a 
characteristic  feature  in  the  margin  of  the  basin,  serving  to  show  that,  in  a 
general  way  at  least,  the  trougli  existed  with  something  like  its  present 
horizontal  limits  as  early  as  the  time  of  the  Coal  Measures.  Ai  no  other 
point  are  the  evidences  as  to  the  conditions  under  which  the  deposits  were 
laid  down  so  clear,  or  at  least  so  well  ascertained,  as  at  Steep  Brook,  but  at 
all  points  the  facts  show  that  the  matei'ials  composing  the  beds  have  been 
transported  from  a  distance,  and  so  far  as  determined  the  carriage  has  been 
from  the  sides  of  the  basin  toward  its  central  part. 

It  is  important  to  note  that  the  arkose  deposits  of  this  district  appear 
to  have  been  the  first  of  a  series  of  erosional  phenomena  leading  in  the 
end  to  the  formation  of  extensive  conglomerates.  The  stages  are,  first,  the 
arkose  material,  or  the  waste  of  rocks  decayed  in  place;  next,  the  clays  and 
sands,  which  may  be  regarded  as  the  product  of  ordinary  erosion,  when 


EFFECTS  OF  EAINFALL  ON  EOCK  DECAY.  55 

the  abrasive  forces  keep  pace  with  the  agents  of  decay;  and  finally,  the 
conglomerates,  formed  when  the  abrasive  actions  go  forward  more  rapidly 
than  those  which  lead  to  the  general  softening  of  the  rocks.  . 

RELATION  OF  ARKOSES  TO  EROSION. 

The  above-mentioned  facts  concerning  the  snccession  of  beds  in  the 
Narragansett  Basin  clearly  point  to  the  existence  of  what  may  be  tei'med  a 
cycle  of  erosion  dependent  on  the  relative  rate  at  which  the  two  diverse 
processes  connected  with  the  decay  of  the  lands  go  forward.  This  equation, 
in  a  general  way,  seems  to  be  as  follows:  Where  the  rainfall  is  so  slight 
that  a  vegetal  covering  is  not  established  in  a  countr}^,  the  chemical  assault 
on  the  rocks,  which  is  due  in  the  main  to  the  CO2  and  other  products  which 
the  decaying  organic  matter  in  the  soil  contributes  to  the  ground  water,  is 
probably  wanting.  The  result  is  that  the  erosive  work,  or  that  which  oper- 
ates to  remove  the  detritus  in  the  form  of  visible  sediment,  though  it  may 
be  very  slight,  is  likely  to  be  enough  to  keep  the  rocks  which  have  been 
softened  well  cleared  away.  In  such  an  arid  country  the  rainfall  is  apt  to 
be  irregularly  distributed,  so  that  the  torrent  action  is  at  times  exceedingly 
strong.  The  result  of  this  is  that  the  valleys  become  encumbered  with 
angular  breccia-like  debris,  such  as  now  exists  in  the  valleys  of  the  arid 
districts  of  the  Cordilleras. 

An  increase  in  the  rainfall  to  the  point  where  an  ample  mantle  of 
vegetation  is  supplied,  but  short  of  the  point  where  torrent  action  is  made 
excessive,  tends  to  produce  a  greater  amount  of  decayed  rock  than  can 
be  cleared  away.  The  result  is  that  the  coating  of  what  we  may  term  the 
the  nontransported  arkose  steadily  increases  in  amount.  The  thicker  this 
porous  layet  becomes  the  more  the  rate  of  the  torrent  action  approaches 
uniformity,  for  the  reason  that  the  open  structure  of  the  decayed  rock  causes 
the  corroded  zone  to  be  an  effective  storehouse  for  the  ground  water,  whence 
it  is  slowly  yielded  to  the  streams.  With  an  increase  in  the  rate  of  precipi- 
tation beyond  the  point  where  the  water  can  be  taken  into  the  unoccupied 
detrital  layer  a  critical  point  is  soon  reached  where  the  mechanical  erosion 
will  rapidly  increase  and  will  gain  on  the  process  of  interstitial  decay.  If 
the  rate  of  mechanical  wear  much  exceeds  that  of  the  decay,  the  result  will 
be  the  deportation  of  solid  waste  in  the  form  of  pebbles,  the  process  being 
marked  in  a  geological  way  by  the  production  of  conglomerates. 


56  GEOLOGY  OF  THE  NAEEAGANSETT  BASIN. 

We  thus  see  that  in  the  erosional  history  of  a  region  wherein  the  rain- 
fall varies  from  zero  to  the  highest  measure  which  we  can  expect,  say  over 
1 00  inches  per  annum,  we  may  look  for  a  series  of  efiFects  which  will  mark 
themselves  in  diverse  classes  of  debris.  So  long  as  the  decay  keeps  in 
general  ahead  of  the  abrasional  work,  the  waste  which  goes  forth  through 
the  streams  is  likely  to  be  of  a  finely  divided  nature,  giving  rise  to  clayey 
slates  as  the  natural  product.  If  a  stream  yields  abundant  materials  which 
would  form  arkose,  it  is  because  the  erosion  is  gaiiaing  on  the  decay.  If 
the  work  produces  pebbles,  the  indication  is  that  the  jnechanical  erosion  is 
so  great  that  wearing  by  solution  plaj's  no  important  part  in  the  process. 

In  this  connection  it  Avill  be  well  to  note  yet  further  that  the  large 
production  of  pebbles  within  a  short  time  can  scarcely  be  accounted  for 
except  on  tlie  supposition  that  the  abrasion  has  been  brought  about  by  the 
action  of  glacial  ice.  As  the  importance  of  this  proposition  has  not  been 
appreciated  by  those  who  have  dealt  with  the  problems  afforded  by  con- 
glomerate deposits,  we  must  note  that  there  are  but  three  ways  in  which 
waterworn  pebbles  can  be  made  in  sufficient  quantities  to  afford  materials  for 
ordinary  conglomerates.  The  first  and  practically  the  only  effective  means 
by  which  pebbles  can  be  extensively  made — i.  e.,  in  large  amount  per  unit 
of  surface  over  a  large  area — is  by  glacial  action.  Where  the  precipitation 
of  a  country  goes  off  as  an  ice  sheet,  every  portion  of  the  rocks  over  which 
it  flows,  if  the  material  be  sufficiently  hard,  becomes  a  part  of  a  vast 
bowlder  factory — for  such,  in  fact,  is  all  the-base  on  which  the  glacier  rests. 
As  the  average  thickness  of  the  till  covering  in  the  glaciated  district  of  this 
country  is  not  less  than  10  feet,  and  as  the  greater  part  of  this  till  is  bowl- 
ders, it  is  clear  that  ice  in  motion  is  specially  adapted  to  forming  such  partly 
rounded  bits  of  stone.  The  materials  in  our  eskers  show  how  successful 
the  subglacial  torrents,  with  their  currents  impelled  by  hydrostatic  pressure, 
were  in  completing  the  rounding  of  pebbles  which  the  ice  began  to  shape. 

When  the  rainfall  of  a  country  goes  to  the  sea  in  a  fluid  state,  the  tor- 
rent section  of  its  river  system,  provided  the  rate  of  decay  is  swift,  is  likely 
to  be  the  seat  of  the  production  of  a  considerable  amount  of  pebbly  mate- 
rial. Yet  the  share  of  the  energy  of  the  portion  of  the  rain  water  which 
is  then  effectively  applied  to  joebble  making  is  but  a  small  fraction  of  what 
is  used  when  the  same  amount  of  precipitation  g'oes  to  the  sea  in  the  form 
of  a  glacier.     Moreover,  the  pebbles  which  are  thus  formed  in  ordinary  tor- 


CONDITIONS  OP  PEBBLE  MAKING.  57 

rents  are  made  in  small  quantities.  No  sooner  does  a  torrent  bed  become 
loaded  with  this  detritus  than  it  ceases  to  be  an  effective  factory  of  the 
rounded  bits  of  stone.  Furthermore,  the  pebbles  which  are  formed  in  tor- 
rent beds  rarely  attain  the  sea  or  any  position  where  they  can  be  built  into 
extended  beds  of  conglomerate.  Although  I  have  inspected  several  thou- 
sand miles  of  seashore,  much  of  it  along  mountainous  coasts,  I  have  never 
found  a  place  where  pebbles,  such  as  are  found  in  the  conglomerates  of 
the  Narragansett  Basin,  from  a  stream  of  any  size  were  entering  the  sea. 
It  may,  indeed,  be  regarded  as  rare  for  a  stream  to  discharge  into  the  ocean 
pebbles  exceeding  an  inch  in  diameter.  To  do  such  work  it  would  have  to 
flow  at  a  torrential  rate  at  its  very  mouth,  a  condition  which  can  be  found 
in  certain  fresh-water  lakes,  but  is  rarely  seen  on  the  ocean  coast  line. 

The  third  means  of  pebble  making  may  be  seen  along  the  seashore 
where  the  waves  are  attacking  hard  rock  cliffs.  In  such  conditions  pebbles 
are  formed,  but  they  are  rarely  accumulated  in  large  quantities ;  in  general 
the  fate  of  coast-made  pebbles  is  to  be  worn  out  by  the  action  of  the  forces 
which  have  shaped  them.  There  are  no  agents  whereby  siich  marine 
pebbles  in  considerable  quantities  can  be  carried  out  for  any  distance  from 
the  shore.  In  rare  cases  ice  forming-  along  the  coast  is  likely  to  inclose 
some  portion  of  the  shore  debris;  this  shore  ice  may  then  drift  out  to  sea 
and  there  deposit  the  load  of  pebbles  which  it  has  rafted.  This  action, 
though  sufficient  to  strew  the  sea  floor  with  shore-made  stones,  can  not  be 
looked  to  as  a  means  of  accumulating  conglomerates. 

The  above-mentioned  considerations  make  it  clear  that  it  is  not  easy 
to  account  for  the  existence  of  widespread  deposits  of  pebbles  of  consid- 
erable size  accumulated  in  massive  strata,  which  in  the  case  of  the  beds  of 
the  Narragansett  field  contain  perhaps  more  pebbles  than  exist  on  the  beaches 
of  the  Atlantic  coast  or  in  all  the  torrent  beds  of  the  Appalachian  Moun- 
tains. The  easiest  way,  if  not  indeed  the  only  way,  to  explain  the  forma- 
tion of  extensive  conglomerates  is  as  follows:  On  the  surface  of  a  land  area 
there  must  first  be  accumulated  a  considerable  deposit  of  rock  fragments, 
such  as  is  normally  gathered  at  the  close  of  a  glacial  period,  or  such  as 
occupies  a  region  of  high  relief,  scanty  rainfall,  and  much  frost  work,  after 
the  manner  of  large  areas  in  the  Cordilleras  and  in  other  parts  of  the  world 
where  these  conditions  exist.  If,  now,  such  a  fragment-strewn  district  is 
gradually  lowered  through  the  mill  of  a  shore  line  either  of  the  sea  or  of  a. 


58  GEOLOGY  OF  THE  NAERAGANSETT  BASIN. 

considerable  lake,  the  chance  for  the  formation  of  normal  conglomerates 
will  be  provided.  The  unorganized  debris  of  the  surface  will  be  taken  to 
pieces  and  recomposed  into  stratified  beds,  as  is  now  being  done  with  the 
glacial  debris  along  the  shores  about  the  North  Atlantic.  In  this  formative 
process  the  pebbles  are  likely  to  be  changed  in  shape  and  assorted  as  to 
size  in  a  way  which  at  once  distinguishes  the  strata  into  which  they  are 
built  from  the  beds  of  till  or  of  residual  breccia  from  which  the  fragments 
were  derived. 

There  are  certain  tests  of  some  value  in  distinguishing  the  conglom- 
erates made  from  rearranged  glacial  materials  from  those  which  owe  their 
formation  altogether  to  marine  action.  Pebbles  made  from  fragments 
which  have  long  been  separated  from  the  bed  rock  are  generally,  unless 
they  be  of  quartz,  much  affected  by  decay;  they  contrast  distinctly  with 
the  fresh  quality  of  the  ordinary  glaciated  pebbles.  As  I  have  observed 
in  the  southern  part  of  this  country,  as  well  as  in  southern  Europe,  the 
detrital  waste  which  comes  into  the  streams  is  generally  so  penetrated  by 
decay  that  it  can  not  be  made  into  pebbles ;  if  perchance  it  holds  together 
in  the  shaping,  the  eye  at  once  separates  the  bit  from  those  which  are  made 
from  freshly  riven  stone. 

Where  pebbles  are  made  by  wave  action  alone,  it  is  a  notable  fact  that 
they  exhibit  very  little  diversity  in  form;  they  are  almost  invariably  sphe- 
roidal, and  when  they  are  accumulated  in  considerable  numbers  the  litho- 
logical  diversity  of  the  material  is  small.  Although  glaciated  pebbles  are 
apt  to  be  somewhat  altered  from  their  original  subangular  shapes  as  they 
pass  through  a  surf  line,  many  of  them,  as  we  may  note  along  the  New 
England  coasts,  will  withstand  a  deal  of  hammering  without  losing  the  dis- 
tinct mark  which  the  ice  work  impressed  upon  them.  Moreover,  taken  col- 
lectively, whether  in  the  original  till  or  in  the  partly  masked  shore  deposits, 
they  commonly  exhibit  a  large  petrographical  range  of  material.  The  facts 
which  are  available  for  the  interpretation  of  conglomerates  show  that  those 
of  the  Narragansett  Basin  are  of  what  we  may  term  secondary  glacial 
origin.  This  is  indicated  by  their  frequent — Indeed,  we  may  say  usual — sub- 
angular  form,  their  petrographical  variety,  and  the  very  small  amount  of 
decay  which  had  affected  the  rock  masses  after  they  left  their  original  bed- 
ding places  and  before  they  were  deposited  in  the  situations  in  which  we 
now  find  them. 


EVIDENCE  FROM  CONGLOMERATES.  59 

The  hypothesis  that  the  coiaglomerates  of  the  Cambrian  and  Carbon- 
iferous as  exhibited  in  this  locaHty  are  the  -results  of  glacial  action  is  sup- 
ported by  the  general  distribution  of  such  deposits  in  this  and  other 
countries.  Massive  conglomerates  of  great  areal  extent  are  distinctly  more 
common  in  high  than  in  low  latitudes.  With  rare,  and  in  most  cases 
questionable,  exceptions  the  deposits  of  this  nature  which  can  be  traced 
horizontally  for  a  great  distance  from  north  to  south  fade  away  as  they 
approach  the  equator.  As  our  study  of  conglomerates  advances,  more  of 
the  deposits  are  found  to  aiford  evidence  as  to  the  glacial  origin  of  their 
pebbles.  The  great  conglomerates  at  the  base  of  the  Carboniferous  in 
India,  which  from  their  interstratified  position  appeared  not  to  be  open  to 
the  explanation  which  has  been  advanced  in  this  writing,  have  recently 
afforded  clear  evidence  to  show  that  glaciation,  possibly  occurring  at  a 
time  when  the  area  was  elevated  to  a  great  height  above  the  sea,  suffi- 
ciently accounts  for  the  origin  of  the  pebbles  and  bowlders  which  the  beds 
contain. 

Although  this  is  not  the  place  for  an  extended  discussion  of  the  matter, 
it  may  be  worth  while  to  remai-k  that  a  collation  of  the  recent  studies  on 
conglomerated  deposits  clearly  shows  that  we  are  fast  approaching  the 
point  where  beds  of  this  nature  will  be  taken  as  presumptive  evidence  of 
glacial  action  occurring  at  the  time,  of  their  deposition,  or  perhaps  imme- 
diately jJi'eceding  it. 

RECORD   VALUE   OF   COISTGIjOMERATES. 

In  connection  with  these  considerations  relating-  to  conglomerates,  it 
may  be  well  to  note  that  deposits  of  this  nature  have  another  much  neg- 
lected element  of  value  to  the  geologist,  in  that  they  afford  him  an  opportu- 
nity to  ascertain  many  facts  concerning  the  physical  conditions  of  the  region 
in  which  they  occur  at  the  time  of  their  formation.  Although  the  value  of 
these  indications  is  in  good  part  self-evident,  they  have  been  so  generally 
neglected  that  it  is  worth  while  to  dwell  upon  the  methods  of  using  them 
and  to  illustrate  them  by  a  special  study  of  the  Narragansett  field. 

If  a  conglomerate  has  not  been  subjected  to  metamorphic  action 
sufficient  to  change  the  original  character  of  its  jaebbles,  these  fragments 
may  be  taken  as  evidence  concerning  the  state  of  the  rocks  whence  they 
came  at  the    time  the    j)ebbles   were   brought  together.      This   evidence. 


(50  GEOLOGY  OF  THE  NAREAGANSETT  BASIN. 

when  examined,  is  seen  to  go  very  far,  and  in  several  directions.  In  the 
first  place,  the  conglomerate  may  be  taken  as  representing  the  beds  which 
were  exposed  to  erosion  at  the  time  it  was  formed.  If  the  beds  are  of 
ancient  and  of  known  age,  they  may  enable  us  to  determine  the  former 
existence,  in  the  field,  of  rocks  which  have  since  disappeared  by  erosion, 
been  lowered  beneath  the  sea  level,  or  been  covered  over  by  other  deposits. 
Thus,  in  the  case  of  the  Carboniferous  conglomerates  of  the  field  under 
consideration,  we  find  in  the  beds  a  very  great  immber  of  quartzitic  pebbles 
which  contain  fossils  evidently  of  the  Cambrian  age.  It  is  clear  that  the 
field  occupied  by  the  quartzites  was  extensive,  for  the  fragments  which 
appear  to  be  of  that  group  of  rocks,  though  not  always  containing  fossils,  are 
about  the  most  numerous  of  the  components  which  make  up  some  of  the 
thickest  layers  of  the  Carboniferous  conglomerates.  A  carefiil  search  of  the 
rocks  of  eastern  Massachusetts  has  failed  to  reveal  the  source  of  these  fossil- 
bearing  pebbles.  Strata  perhaps  about  the  same  age  are  found  in  various 
parts  of  eastern  Massachusetts,  but  they  are  lithologically  and  in  fossil  con- 
tents very  different  from  the  strata  which  afforded  the  pebbles.  While  it  is 
possible  that  the  field  whence  the  quartzite  bits  came  has,  by  differential 
warping,  been  carried  beneath  the  sea,  it  is  rather  improbable  that  such  has 
been  the  case;  it  is  more  likely  that  the  rocks  in  question  lay  on  the  margin 
of  the  basin,  whence  by  erosion  they  have  disappeared. 

It  is  a  noteworthy  fact  that  the  above-mentioned  quartzite  is  the  only 
rock  of  the  many  contained  in  the  Carboniferous  conglomerates  which  has 
disappeared  from  this  part  of  the  country  since  these  beds  were  formed. 
There  are,  it  is  true,  certain  uncharacteristic  sandstone  pebbles  which 
can  not  clearly  be  identified  with  anything  now  in  or  about  the  basin,  but 
these  are  not  numerous.  The  impression  left  by  the  stud}'  of  the  Coal 
Measures  pebbles  is  that  the  general  character  of  the  rocks  exposed  at  the 
surface  in  this  field  in  Carboniferous  time  was  substantially  the  same  as 
that  of  the  rocks  remaining  at  the  present  time.  This  view  is  justified  by  a 
comparison  of  the  materials  contained  in  the  ancient  and  the  modern  aggre- 
gations of  glacial  waste.  Taking  pains  to  exclude  from  the  waste  of  the 
last  Glacial  period  the  pebbles  which  have  been  worn  from  the  basin  rocks 
of  this  field,  the  observer  is  at  once  struck  with  the  likeness  of  the  two 
assemblages,  a  likeness  which  shows  us  that  the  erosive  agents  found,  with 
the  exception  of  the  above-noted  quartzites,  much  the  same  rocks  open  to 


TIME  OF  METAMOEPHISM.  61 

their  assaults  in  these  two  periods,  which  must  have  been  separated  by 
some  miUions  of  years. 

The  fiekl  open  to  examination  is  much  more  Hmited  in  the  case  of  the 
Cambrian  conglomerates  than  in  that  of  the  Carboniferous  pudding  stones. 
Moreover,  the  pebbles  contained  in  the  beds  have  been  subjected  to  more 
metamorphism.  Nevertheless,  the  studies  which  have  been  made  show  that 
the  rocks  of  the  fundamental  complex  had  attained  about  their  present  con- 
stitution before  the  beginning  of  the  Olenellus  epoch.  These  pebbles  rep- 
resent the  granites,  gneisses,  quartzites,  etc.,  of  the  rocks  which  are  found 
beneath  the  Cambrian  beds,  and  show  that  the  crystalline  condition  of  these 
deposits  was  approximately  the  same  as  it  is  now.  It  is  evident,  however, 
that  there  were  quartzites  and  other  semimetamorphosed  beds  which  afforded 
waste  to  erosion  in  the  Olenellus  epoch,  beds  which  are  not  recognizable  as 
in  place  in  the  district,  and  which  perhaps,  like  those  noted  in  connection 
with  the  Carboniferous,  have  disappeai-ed  from  the  district.  It  is  neverthe- 
less clear  that  the  greater  part  of  the  crystalline  rocks  of  this  district  were 
already  not  only  in  their  present  mineralogical  condition,  acquired  during  a 
period  when  they  had  been  deeply  buried  beneath  other  rocks,  but  had  been 
stripped  by  the  erosive  forces  of  this  ancient  covering. 

It  must  not  be  supposed  that  the  whole  or  even  the  greater  part  of 
the  metamorphism  which  has  taken  place  in  this  region  had  been  accom- 
plished by  Cambrian  or  even  Carboniferous  time.  While  in  certain  districts 
and  with  certain  rocks  this  work  seems  to  have  been  then  completed,  or 
nearly  so,  in  other  parts  of  the  field  the  action  continued  at  least  until  after 
the  deposition  of  the  Coal  Measures  strata.  Thus  the  beds  of  the  last- 
named  series  in  the  region  about  Worcester  and  in  that  about  Wickford 
have  been  transformed  to  gneisses  which,  but  for  collateral  evidence,  could 
not  be  recognized  as  having  been,  in  their  original  state,  the  associates  of 
ordinary  coals.  It  is  evident  that  in  this  last-named  field  the  process  of 
metamorphism  has  gone  on  with  exceeding  irregularity,  certain  parts  of  the 
most  ancient  deposits — as,  for  instance,  the  fossiliferous  strata  of  the  Olenellus 
horizon — being  not  much  altered  beyond  the  induration  common  to  all 
ancient  flaggy  layers,  while  bat  a  few  miles  away  cong-lomerates  have  been 
so  far  converted  into  crystalline  rocks  that  the  original  character  of  the  beds 
has  been  almost  completely  lost. 


Q2  GEOLOGY  OF  THE  NAERAGANSETT  BASIN. 

RED  COiOR  OF  THE  CAMBRIAN  AND  THE  CARBONIFEROUS. 

The  red  hue  of  certam  portions  of  the  Cambrian  as  well  as  of  the 
Carboniferous  rocks  affords  a  matter  for  inquiry.  Though  no  solution  of 
the  problem  has  been  attained,  it  may  be  well  to  note  certain  facts  of  possi- 
ble value  to  those  who  may  hereafter  attack  the  question.  It  is  noteworthy 
that  the  red  beds  of  both  the  above-mentioned  series  occur  on  the  western 
and  northern  sides  of  the  Narragansett  Basin  and  in  the  trough  of  the 
Norfolk  Basin.  In  both  these  sections  the  red  beds  are  somewhat  irregu- 
larly distributed,  generally  occurring  between  deposits  which  have  no  trace 
of  the  peculiar  hue.  In  some  cases,  as  noted  by  Mr.  Woodworth,  the  red 
stratum  may  be  but  a  few  inches  thick,  lying  between  sandstones  or  arkoses 
of  a  whitish  hue.  This  peculiarity  of  distribution  is  also  very  noticeable 
in  deposits  exhibited  at  Gay  Head  and  elsewhere  on  Marthas  Vineyard 
which,  in  Cretaceous  and  Tertiary  time,  were  made  under  conditions  some- 
what similar  to  those  which  existed  in  the  earlier  periods  when  the  Narra- 
gansett  deposits  were  formed. 

It  seems  likely  that  the  red  hue  of  stratified  deposits  is  due  to  a  variet}" 
of  actions.  In  some  instances,  as  along  the  present  coast  Ihie  of  the  region 
and  about  the  mouth  of  the  St.  Lawrence,  red  beds  may  be  formed  by  the 
disintegration  of  Triassic  or  other  red  sandstones  and  clays,  the  rearranged 
material  retaining  in  large  measure  the  hue  of  the  rocks  Avhence  the  d(ibris 
came.  In  other  instances,  perhaps  in  the  case  of  the  Cambrian  and  possi- 
bly the  Carboniferous  of  the  Narragansett  field,  the  red  hue  may  be  due  to 
the  fact  that  the  beds  thus  colored  originally  contained  a  share  of  lime  car- 
bonate. Downward-percolating  waters  containing  iron  oxide  transformed 
these  beds  first  into  impure  siderite,  and  further  change  served  to  bring  the 
iron  into  the  state  of  limonite.  The  coloration  thus  brought  about  is  fre- 
quently to  be  observed  in  the  Devonian  and  Silurian  rocks  of  the  Appala- 
chian district,  being  particularly  conspicuous  in  the  iron-bearing  members 
of  the  lower  Devonian  and  ujjper  Silurian  strata  of  eastern  Kentucky,  as 
for  instance  in  Bath  County.  In  yet  other  instances  the  decay  of  crystal- 
line rocks  containing  a  considerable  share  of  iron  may  have  provided  the 
ferruginous  mateiial  in  a  direct  manner  in  the  process  of  sedimentation. 
Some  unpublished  studies  as  to  the  amount  of  magnetic  oxide  in  the  drift 
covering  which  exists  in  this  part  of  New  England  have  shown  me  that  the 


EED  COLOE  OF  CAMBRIAN  AKD  CARBONIFEROUS.  63 

propoi'tion  of  this  material  ranges  from  about  one-half  of  one  per  cent  to 
as  much  as  five  per  cent  by  weight  of  the  mass.  As  further  oxidation  of 
these  crystals  of  magnetic  iron  goes  on  but  slowly,  the  deposits  in  which 
they  finally  come  to  rest  may  contain  a  large  share  of  the  material  which  is 
to  be,  by  fuii;her  change,  dissolved  and  distributed  through  the  bed.  Even 
where  the  ferruginous  matter  has  been  accumulated  between  the  fragments 
of  rock  in  the  form  of  a  thin  vein  or  coating  separating  the  bits,  it  may  by 
a  further  process  of  change  lose  the  iron  in  a  greater  or  less  measure  and 
become  a  mere  stain. 


CHAPTER    III. 

GLACIAL  HISTORY  OF  THE  NARRAGANSETT  BASIN. 

The  interpretable  history  of  this  basin,  so  far  as  it  has  depended  on  the 
action  of  ordinary  streams  and  of  the  sea,  has  ah-eady  been  set  forth.  This 
account  of  the  effects  of  the  solar  energy  which  has  been  appHed  through 
the  atmosphere  needs  to  be  supplemented  by  some  consideration  of  the 
work  which  was  done  during  the  Glacial  periods.  The  account  which  will 
here  be  given  of  the  work  will  in  the  main  be  restricted  to  the  phenomena 
that  are  in  some  measure  peculiar  to  the  field,  for  the  reason  that  the  surface 
geology  of  New  England  is  to  be  the  subject  of  a  separate  publication  by 
the  Geological  Survey.  Any  full  discussion  of  these  matters  in  this  memou- 
woidd  therefore  involve  ah  undesirable  repetition. 

We  may  first  note  that  the  deposits  formed  during  the  times  repre- 
sented by  the  conglomerates  of  the  Carboniferotis  series  have  a  character 
which  warrants  the  hypothesis  that  they  are  to  a  considerable  extent  the 
products  of  glacial  action.  The  view  that  this  age  was  a  period  of  recurrent 
ice  work  has  already  been  ably  presented  by  the  late  Dr.  James  CroU. 
Here,  as  elsewhere  along  the  Appalachian  district,  the  supposition  is  sup- 
ported by  an  array  of  facts  which  deserve  more  attention  than  they  have 
received.  These  facts,  as  they  are  exhibited  in  the  country  from  Alabama 
to  the  St.  Lawrence,  will  be  briefly  set  forth. 

CARBONIFEROUS   COXGIiOMERATES. 

In  the  Southern  States  the  conglomerates  of  the  Carboniferous  periods 
are,  with  rare  and  unimportant  exceptions,  made  up  of  pebbles  of  quartz, 
which,  as  has  been  noted  by  several  observers,  are  evidently  the  remains 
of  the  uudecayed  veinstones  that  survived  the  decay  which,  in  the  pre- 
Carboniferous,  as  in  the  modem  time,  greatly  aff"ected  the  rocks  that  were 
exposed  to  the  atmospheric  agents.     The  great  thickness  of  these  quartz 


(JAHBOMFKRUUS  CONGLOMEHATivS.  '   (55 

couglomerates,  their  wide  distribution,  as  well  as  the  general  absence  of 
fossil  remains,  are  best  explained  on  the  supposition  that  the  erosion 
took  place  in  an  ice  time,  being  effected  by  the  glaciers  or  by  the  currents 
of  living  water  which  coursed  beneath  them.  In  no  way  save  by  com- 
paring this  ancient  work  with  that  now  in  progress  in  glaciated  regions  can 
we  well  account  for  the  deposition  of  the  Millstone  grit  of  the  Southern 
Appalachians. 

As  we  go  northward  from  the  valley  of  the  Tennessee  the  Carbonifer- 
ous strata  show  an  increasing  amount  of  pebbly  material  which  has  been 
derived  from  the  undecayed  bed  rocks.  As  elsewhere  noted,  these  rocks 
indicate  that  there  was  at  the  beginning  of  the  period  a  considerable  thick- 
ness of  decayed  material,  but  before  long  the  erosive  agents  had  removed 
this  friable  mass,  and  thereafter  the  supply  of  pebbly  matter,  vast  in  amount, 
was  obtained  by  the  breaking  up  of  bed  rocks  which  show  no  evidence 
that  they  had  been  affected  by  superficial  decay.  As  we  go  yet  farther 
north,  in  the  next  field  where  the  rocks  of  this  age  appear,  i.  e.,  in  the  region 
about  the  south  shore  of  the  St.  Lawrence,  the  thickness  of  the  conglomer- 
ate even  exceeds  that  of  the  sections  hereafter  to  be  described  in  the  north- 
ern part  of  the  Narragansett  Basin.  In  a  word,  the  facts  make  it  evident 
that  the  Carboniferous  period  of  the  eastern  part  of  North  America,  like 
certain  other  periods,  was  one  of  exceedingly  rapid  alternations  between  the 
conditions  which  favored  the  development  of  marsh  vegetation  and  others 
under  which  the  accumulations  of  coarse  sedimentary  deposits  went  on  with 
great  rapidity. 

Although  there  are  instances  in  which  a  torrent  may  accumulate  a 
large  detrital  cone  composed  of  bowlders  and  pebbles,  I  know  of  no  geo- 
logical machinery  now  at  work  on  the  earth's  surface,  or  which  can  reason- 
ably be  supposed  to  have  operated  in  the  past,  except  glaciation,  that  is 
competent  to  produce  such  immense  masses  of  coarse  detritus  as  are  contained 
in  these  conglomerates,  or  bring  them  into  position  where  water  action  can 
effect  their  arrangement  into  beds.  The  area  of  the  deposits  lying  on  the 
two  sides  of  the  old  Appalachian  axis  probably  now  exceeds  60,000  square 
miles;  the  average  thickness  of  the  section  is  certainly  not  less  than  2,500 
feet;  so  that  the  amount  of  matter  of  a  prevailingly  coarse  nature  which 
was  laid  down  along  the  old  Appalachian  ridge  in  a  period  apparently  of 
no  great  duration  was  not  less  than  20,000  cubic  miles,  and  probably  was 
MON  xxxiii 5 


QQ  GEOLOGY  OF  THE  NARRAGANSETT  BASIX. 

far  more  than  that  amount.  When  we  remember  that  the  whole  drainag'e 
basin  of  the  Mississippi — a  region  which  is  probably  many  times  as  great 
as  the  field  whence  this  detritus  came — yields  to  erosion  not  more  than 
about  a  twentieth  of  a  cubic  mile  each  year,  it  becomes  evident  that  we 
have  to  bring  into  our  conception  of  the  causes  operating  in  the  olden  day 
some  more  effective  agent  of  erosion  than  is  found  in  free  water. 

If  all  the  detritus  of  the  Carboniferous  conglomerates  were  of  the  same 
nature  as  that  which  is  found  in  the  Southern  Millstone  grit  and  the  related 
beds,  we  could  perhaps  assume  that  their  production  was  due  to  the  invasion 
of  the  sea  acting  upon  a  deep  decayed  zone,  but  the  fact  that  the  thickest  of 
these  deposits  occur  in  the  northern  part  of  the  Appalachian  field  and  are 
composed  of  undecayed  pebbles  negatives  this  hypothesis  and  requires 
us  to  assume  that  the  erosion  attacked  the  bed  rock  with  great  intensity. 
That  this  attack  was  by  torrent  action  is  extremely  improbable;  for,  as 
before  stated,  no  torrents  are  now  known  to  produce  so  large  amounts  of 
pebbles  of  crystalline  rocks  as  were  formed  at  this  time;  and  when  such 
fragments  are  formed,  so  far  as  my  observations  go,  they  always  present 
marks  of  decay,  due  to  the  slow  manner  in  which  they  are  shaped  and  to 
the  conditions  of  their  storage  in  detrital  cones.  The  pebbles  of  the 
Narragansett  and  other  conglomerates  of  the  same  age  which  I  have 
examined,  even  those  of  a  compound  nature,  are  in  practically  all  cases  as 
fresh  as  those  contained  in  the  bowlder  deposits  which  were  formed  during 
the  last  Glacial  period.  This  appears  to  negative  the  supposition  that  they 
could  have  been  the  result  of  ordinary  torrent  action  and  to  require  a 
method  of  formation  which  apparently  can  be  explained  on  the  hypothesis 
of  glacial  erosion. 

It  should  be  noted  that  the  pebbles  of  the  Carboniferous  conglomerates, 
especially  in  the  Narragansett  district,  show  no  trace  of  glacial  scratches; 
moreover,  they  generally  have  a  rather  rounded  form  and  are  of  less  varied 
size  than  those  in  any  of  the  till  deposits  formed  during  the  last  Glacial 
period.  In  some  cases,  however,  they  seem  to  me  to  retain  the  faceted 
shape  which  is  so  characteristic  of  ice-made  pebbles.  When  compared  with 
the  pebbles  of  the  last  Glacial  period,  which,  in  a  measure,  have  been  sub- 
jected to  marine  or  stream  action,  they  are  found  to  coiTcspond  with  them 
in  all  essential  features,  except  when,  as  is  often  the  case,  the  old  fragments 
have  been  deformed  by  stresses  which  came  upon  them  since  they  were 


GLACIAL  PHENOMENA.  67 

built  into  the  Carboniferous  strata.  The  absence  of  large  bowlders  in  the 
Carboniferous  is  paralleled  by  what  we  find  in  the  modern  washed  drift; 
there,  as  might  be  expected,  the  larger  fragments  have  been  kept  out  of  the 
beds  by  the  sorting  process  which  takes  place  in  water  transportation. 

The  facts  disclosed  by  a  study  of  the  conglomerates  of  this  basin  lead 
to  the  conclusion  that  the  pebbles  were  probably  formed  by  glacial  action, 
and  that  the  fragments  were  brought  to  their  pi-esent  position  by  torrents 
which  swept  into  the  basin  from  the  highlands  that  bordered  it.  Their 
transportation  to  their  present  sites,  as  well  as  their  distribution  into  beds, 
may  have  been  due  to  waves  and  shallow-water  currents  acting  during  a 
period  of  increasing  depression  of  the  land.  In  no  way  save  by  glacial 
work  does  it  seem  to  me  possible  to  account  for  the  rapid  formation 
of  the  great  mass  of  pebbly  detritus  which  is  contained  in  these  beds.  It 
therefore  may  fairly  be  held  that  the  Carboniferous  period,  in  this  district 
at  least,  was  one  of  extensive  and  long-continued  glacial  action,  and  that 
the  greater  part  of  the  section  exhibited  in  the  basin  is  made  up  of  rocks 
which  owe  their  more  important  features  to  the  action  of  glaciation.  From 
the  Carboniferous  to  the  Pleistocene  this  area  affords  no  evidence  of  ice 
action. 

liAST    GliACIAI.    PERIOD. 

The  last  Glacial  period  has  left  upon  this  district  marks  of  its  action 
which  are  as  indubitable  as  any  that  are  found  in  the  region  to  the  north- 
ward. In  the  time  of  the  greatest  southward  extension  the  front  of  the  ice 
evidently  lay  considerably  to  the  south  of  the  whole  southern  shore  of  Mas- 
sachusetts, Rhode  Island,  and  Connecticut.  This  is  shown  by  the  presence 
of  extensive  moraines  on  the  Elizabeth  Islands,  Marthas  Vineyard,  and  Nan- 
tucket, as  well  as  on  Long  Island,  New  York.  A  careful  inspection  of  the 
marine  soundings  off  this  shore  has  failed  to  reveal  any  indications  of  a 
submerged  moraine  marking  the  extreme  line  to  which  the  ice  sheet 
attained.  Moreover,  the  evidence  gained  by  the  study  of  the  front  over 
the  land  from  the  coast  of  New  Jersey  to  the  far  West  goes  to  show  that 
the  extreme  extension  of  the  ice  was  of  a  very  temporary  character,  the 
considerable  halts  having  taken  place  in  the  stages  of  retreat  which  probably 
began  very  shortly  after  the  farthest  southward  advance  had  taken  place. 

The  stages  of  retreat  of  the  glacier  in  and  near  the  Narragansett  Basin 
are   fairly  well    marked   by  the    occurrence  of  frontal  moraines.     These 


gg  GEOLOGY  OF  THE  NARRAGANSETT  BASIN. 

moraines  consist  in  part  of  ridges  composed  of  glacial  waste,  in  charac- 
teristic, irregular,  shoved  attitudes,  each  ridge  with  a  more  or  less  distinct 
sand  plain  or  frontal  apron  on  the  side  which  lay  away  from  the  ice,  and 
in  part  of  bowldery  tracts  where  the  glacier  did  not  build  a  distinct  or 
frontal  wall  or  where  it  may  have  overridden  or  broken  down  the  barrier 
after  its  construction.  It  should  be  noted  that  these  moraines,  unlike 
those  on  Long  Island  and  Marthas  Vineyard,  are  not  placed  at  right 
angles  to  the  general  trend  of  the  ice  movement,  but  on  the  west  side 
of  Narragansett  Bay  are  turned  into  a  nearly  north-and-south  position. 
Beyond  the  head  of  the  bay  they  again  turn  more  nearly  to  the  east- 
and-west  direction.  On  the  eastern  side  of  the  basin  the  ridges  are  not 
traceable  with  sufficient  distinctness  for  mapping,  but  the  outlines  of  the 
ice  front  at  the  time  of  the  formation  of  this  moraine  are  well  enough 
shown  to  make  it  plain  that  there  was  a  deep  indentation  at  that  point,  so 
that  while  the  ice  overlapped  the  present  shore  on  either  side  of  the  basin 
the  front  did  not  extend  much  south  of  Taunton.  Such  lobations  of  the 
margin,  as  they  have  been  termed  by  Chamberlin,  were  very  common 
along  the  front  of  the  great  ice  field.  They  are  due  to  irregularities  of 
the  surface  over  which  the  ice  moved  or  to  other  local  conditions.  In  other 
instances  the  presence  of  a  deep,  broad  valley,  such  as  is  afforded  by  the 
channels  of  the  Narragansett  Bay,  led  to  the  projection  of  the  ice  at  its 
mouth  beyond  the  main  line  of  the  front.  In  this  instance  the  retreat  of 
the  front  was  probably  due  to  great  volume  of  the  subglacial  streams  which 
flowed  from  the  areas  to  the  northward.  Their  effect  on  the  ice  at  the 
margin  would  be  to  melt  it  away  at  the  base,  making  the  formation  of  ice- 
bergs an  easy  matter.  As  the  region  was  evidently  depressed  below  its 
present  level  at  the  time  the  ice  was  most  advanced — lowered,  it  may  be,  to 
some  hundi'eds  of  feet  below  its  present  altitude — the  undermining-  action 
of  the  waters  would  naturally  tend  to  detach  bergs. 

It  is  evident  that  the  ice  front  in  the  region  between  the  northern  part 
of  the  basin  and  the  sea  was  subjected  to  many  alternations  of  advance  and 
retreat  which  are  not  registered  in  any  distinct  moraines.  About  twenty 
years  ago,  when  the  Old  Colonj^  Railroad  Company  was  widening  its  road- 
bed, the  new-made  sections  distinctly  showed  that  there  had  been  a  score 
of  these  oscillations  in  the  line  from  North  Easton  to  Somerset,  each  marked 
by  the  disruption  and  erosion  of  the  deposits  which  had  previously  been 


GLACIAL  DEPOSITS.  (>9 

formed  at  the  front  of  the  ice.  The  same  evidence  is  visible  at  the  present 
time,  though  less  distinctly,  in  similar  cuttings  which  are  making  from 
Brockton  southward.  The  result  of  these  irregular  movements  of  the  ice 
has  been  to  give  the  drift  deposits  of  this  field  a  peculiarly  irregular  and 
confused  character.  The  greater  part  of  the  eskers  or  ridg'es  of  sand,  gravel, 
and  bowlders  which  were  formed  within  the  ice-carved  channels  that  were 
excavated  by  the  subglacial  streams  has  been  effaced. 

It  is  a  notable  fact  that  in  the  southern  part  of  the  basin,  on  the  shores 
and  islands  of  that  part  of  it  which  is  included  in  Rhode  Island,  eskers  are 
essentially  absent,  except  near  the  moraine  which  borders  the  western 
margin  of  the  field.  This  seems  to  be  due,  not  to  the  successive  advances 
and  recessions  of  the  ice  front,  but  rather  to  the  fact  that  the  very  deep  chan- 
nels of  the  bay  provided  ample  low  levels  through  which  the  subglacial 
streams  made  their  way  to  the  sea.  In  the  district  between  the  railway 
bridge  at  Somerset  and  Steep  Brook  Station  there  is  an  extensive  and  very 
characteristic  area  of  those  "pitted  plains"  which  are  often  found  near  where 
a  sifbglacial  stream  discharged  its  cu^rrent  into  open  water.  The  area 
which  now  remains  is  evidently  only  a  fragment  of  the  original  field.  The 
materials  seem  to  have  been  brought  to  their  position  by  an  under-ice 
river  which  followed  in  general  the  line  of  the  present  Taunton  River.  The 
cause  of  the  pittings  is  not  yet  determined,  but  they  are  probably  due  to 
the  embedding  of  masses  of  ice  in  the  swiftly  accumulating  detritus,  these 
small  bergs  being  weighted  down  to  the  bottom  by  the  amount  of  rocky 
matter  which  they  contained;  when  they  melted,  the  originally  level 
surface  fell  into  its  present  shape. 

The  till  or  bowlder-clay  coating  of  this  district  is,  on  the  average,  less 
thick  than  in  the  region  lying  immediately  to  the  northward;  wherever  the 
section  extends  to  the  bed  rock  this  most  general  element  of  the  drift — the 
waste  dropped  on  the  rocks  in  the  last  retreat  of  the  ice — is  commonly  found 
to  have  a  thickness  of  less  than  10  feet.  Although  this  till  sheet,  when  it 
covers  rounded  masses  of  the  bed  rocks,  often  takes  on  a  drumlin  aspect,  it 
seems  clear  that  there  are  none  of  these  peculiar  lenticular  hills  in  the  basin. 
Their  absence  on  the  margin  of  this  part  of  the  continental  glacier  is  in 
accord  with  their  distribution  in  other  parts  of  this  country;  they  are 
evidently  due  to  the  conditions  which  prevailed  in  the  portion  of  the  ice 
which  lay  near  the  margin,  but  not  usually  within  50  miles  or  so  of  its  verge. 


70  GEOLOGY  OF  THE  NAliRAGANSETT  BASIN. 

It  is  to  be  noted  that  the  till  materials  of  this  basin  contain  a  much 
smaller  amount  of  clay  than  is  the  case  with  the  like  deposits  farther  inland. 
This  is  probably  due  to  the  fact  that  in  this  marginal  district  the  materials 
composing  the  till  consist  largely  of  esker  and  other  washed  gravels  that 
had  already  lost  their  clay  element.  In  the  irregular  movements  of  the  ice 
and  of  the  subglacial  streams  a  large  part  of  this  clayless  matter  is  brought 
again  into  the  ice,  and  in  the  end  finds  its  way  to  the  surface  in  the  form  of 
till.  The  result  is  that  in  this  marginal  portion  of  the  glacial  field  in  New 
England  there  is  often  little  difference  in  the  materials  which  go  to  make 
up  till  or  kame  deposits,  the  clay  element  having  been  in  both  cases  washed 
away.  The  effect  of  this  is  to  make  the  value  of  the  fields  for  tillage 
much  less  uniform  than  is  the  case  where  the  till  deserves  its  ancient  name 
of  bowlder  clay. 

The  origin  of  the  glacial  detritus  of  the  Narragansett  Basin  has  not 
yet  been  fully  traced.  From  the  studies  which  have  been  made  it  is  suffi- 
ciently evident  that  the  carriage  in  the  case  of  the  materials  contained  in  the 
till  has  in  general  been  for  no  great  distance.  Although,  as  will  hereafter  be 
noted,  there  is  at  least  one  case  where  the  transportation  has  extended  very 
far,  the  evidence  shows  that  at  least  four-fifths  of  the  till  ddbris  has  been 
carried  not  more  than  5  or  6  miles.  This  determination  is  easily  made  on 
the  northern  border  of  the  basin,  where  the  line  between  the  pre-Cambrian 
and  igneous  and  the  Carboniferous  rocks  can  be  traced  with  approximate 
accuracy.  The  materials  which  have  been  conveyed  in  the  subglacial 
streams,  here  as  elsewhere,  have  been  subjected  to  much  greater  transpor- 
tation. The  exact  extent  of  this  has  not  been  determined,  but  it  has 
probably  amounted  to  many  times  the  distance  of  the  carriage  of  the 
materials  which  form  the  till. 

A  large  part  of  the  waste  which  enters  into  the  composition  of  the  drift 
of  this  district  has  come  from  the  disintegration  of  the  conglomerates  of 
the  Carboniferous  section.  This  is  shown  by  the  fact  that  a  considerable 
portion  of  the  drift  pebbles  retain  the  distinct  form  which  was  given  to  them 
by  the  stresses  to  which  they  were  subjected  in  the  beds  in  which  they  had 
lain  so  long,  and  also  by  the  fact  that  these  pebbles  are  often  composed  of 
the  fossiliferous  quartzite  which  yielded  so  much  to  the  debris  in  the  Car- 
boniferous time,  but  does  not  now  exist  in  the  original  bedded  form  in  any 
part  of  the  district.     The  fact  that  the  glacial  deposit  in  the  older  moraines 


GLACIAL  EROSION.  71 

contains  relatively  few  large  bowlders  which  have  been  derived  from  the 
conglomerate,  while  the  pebbles  from  that  source  are  extremely  abundant, 
is  worthy  of  note.  Thus,  on  Marthas  Vineyard,  where  the  bowlders  and 
pebbles  which  lie  on  the  Cretaceous  and  Tertiary  rocks  have  all  been 
imported  from  the  Narragansett  Basin,  the  amount  of  pebbles  which  have 
been  separated  from  the  matrix  of  conglomerate  is  very  great,  but  the 
number  of  bowlders  of  the  conglomerate  rock  is  so  limited  that  an  inspec- 
tion of  a  thousand  of  these  erratics  revealed  only  half  a  dozen  of  this 
nature,  the  others  being  from  the  granitic  and  other  old  rocks  which  form  the 
margins  of  the  basin  or  from  some  of  its  inliers  of  like  rocks.  In  its  ordi- 
nary undecayed  state  the  conglomerate  fractures  in  such  a  manner  that 
the  rift  intersects  the  embedded  pebbles.  We  are  therefore  justified  in 
believing  that  at  the  +ime  the  glacial  flow  began  to  attack  this  region  the 
deposits  were  decayed  to  a  considerable  depth,  so  that  the  attrition  broke 
up  the  adhesions  and  separated  the  pebbles  from  the  matrix.  The  fact  that 
the  bowlders  of  the  massive  conglomerate  are  very  rare  in  the  inoraine  of 
Marthas  Vineyard,  which  was  formed  at  an  early  stage  of  the  ice  time, 
while  they  are  relatively  much  more  common  in  the  drift  lying  in  the  basin, 
gives  stxpport  to  this  view.  It  is  certain  that  the  debris  from  this  basin 
which  is  found  in  Marthas  Vineyard  was  derived  from  the  area  in  the 
earlier  stages  of  the  glacial  excavation,  while  that  formed  on  the  surface  of 
the  conglomerate  represents,  of  course,  the  last  part  of  the  erosion  which 
was  effected. 

AMOUNT  OF  EROSION. 

Although  the  amount  of  erosion  which  was  accomplished  by  the  ice 
in  the  last  Glacial  epoch  can  not  well  be  determined,  the  evidence  goes  to 
show  that  it  was  considerable.  Thus  the  moraines  in  Falmouth  and  on  the 
island  of  Marthas  Vineyard  and  the  Elizabethan  group,  all  of  which  appear 
to  owe  their  materials  in  the  main  to  the  rocks  of  the  basin  and  its  margins, 
contain  in  the  aggregate  a  mass  of  matter  which,  evenly  distributed  over  the 
basin,  would  cover  it  to  the  depth  of  several  feet.  It  is  not  to  be  believed 
that  these  accumulations  represent  anything  like  half  the  rocky  matter 
which  was  worn  away  from  the  Narragansett  district.  Better  evidence 
as  to  the  amount  of  erosion,  as  well  as  much  information  concerning  the 
distance  to  which  the  drift  has  been  carried,  is  afi"orded  by  the  bowlder 
trains  of  this  field.     These  trains  are  traceable  from  certain  of  the  peculiar 


72  GEOLOGY  OF  THE  NAEKAGANSETT  IJASIN. 

deposits  of  the  district  to  distances  which  vary  with  the  endurance  of  the 
particular  kinds  of  rock.  The  crystalhne  hmestones  of  Lincohi  form  trains 
having  a  traceable  length  of  from  4  to  5  miles;  after  a  journey  of  that 
length  the  rather  soft  bowlders  seem  to  be  quite  worn  out.  The  exceed- 
ingly hard  ilmenitic  magnetite  which  occurs  in  Cumberland  near  Woon- 
socket,  Rhode  Island,  has  yielded  the  most  perfect  bowlder  train  that  has 
3'^et  been  traced  in  this  section  of  the  country.  Originating  in  a  deposit 
which  has  a  Avidth  transverse  to  the  path  of  the  ice  of  only  a  few  hundred 
feet,  this  train  extends  in  a  gradually  broadening  path  to  the  outer  or 
southern  part  of  Narragansett  Bay  in  a  nearly  north-and-south  course; 
thence  it  appears  to  have  been  deflected  easterly,  so  that  it  overlapped 
the  western  peninsula  of  Marthas  Vine5^ard,  known  as  Gay  Head.  In  that 
district  foiu-  or  five  specimens  of  the  unmistakable  rock  have  been  found, 
which  afford  sufficient  evidence  that  the  train  extended  at  least  60  miles 
from  the  point  of  origin. 

In  a  description  of  the  Iron  Hill  bowlder  train,^  I  have  given  a  detailed 
account  of  its  phenomena;  and  an  estimate,  based  on  such  data  as  were 
obtainable  that  served  to  show  the  amount  of  the  rock  in  the  deposit,  was 
that  the  amount  of  erosion  which  had  taken  place  at  Cumberland  Hill 
during  the  Glacial  epoch  was  not  less  than  60  feet.  In  reviewing  the  facts, 
it  seems  to  be  evident  that  this  estimate  is  undei'  rather  than  over  the  truth. 
It  is  not  unlikely  that  if  all  the  waste  from  this  elevation  which  was 
removed  by  ice  action  could  be  restored,  the  summit  would  be  near  200 
feet  above  the  present  level.  It  is  not  to  be  supposed  that  the  amount  of 
erosion  in  the  Narragansett  area  was  as  great  as  that  which  occurred  at 
Iron  Hill.  At  the  time  the  ice  began  to  act,  that  mass  was  probably  at  a 
much  higher  level  in  relation  to  the  suiTounding  counti-y  than  it  is  at  pres- 
ent; it  is  likely  that  the  processes  of  decay  had  penetrated  deeply  along  the 
numerous  joints,  so  that  when  assailed  by  the  ice  it  rapidly  broke  up. 
However,  making  what  seems  to  be  all  due  allowance  for  this  probably 
greater  erosion  in  this  point,  it  must  be  confessed  that,  taken  with  the  evi- 
dence before  adduced,  it  serves  to  show  that  a  considerable  thickness  of 
beds,  perhaps  near  100  feet  of  rock,  must  have  been  worn  from  this  area 
during  the  time  the  ice  lay  upon  it. 

'The  conditions  of  erosion  beneatli  deep  glaciers,  Tjased  upon  a  study  of  the  bowlder  train  from 
Iron  Hill,  Cumberland,  Rhode  Island,  by  N.  S.  Shaler:  Bull.  Mub.  Comp.  Zool.  Harvard  Coll.,  Vol. 
XVI,  No.  11,  .January,  1893,  pp.  185-225,  4  pis.  and  map. 


OHANNELS  OF  BAYS.  73 

It  is  well  to  contrast  tlie  rapid  and  effective  erosion  work  of  the  conti- 
nental glacier  with  the  relatively  very  slight  action  that  free  water  or 
atmospheric  decay  has  had  upon  the  rocks  of  this  district  since  the  ice 
mantle  passed  from  its  surface.  Since  the  surface  entered  on  its  present 
state  there  has  been  but  very  little  decay  of  the  rocks.  Even  where  they 
have  remained  without  a  covering  of  soil,  as  is  the  case  in  the  summit  of 
Iron  Hill,  the  penetration  of  decay  in  most  instances  is  inconsiderable,  and 
the  actual  loss  of  material  is  so  slight  that  the  lowering  of  the  surface  has 
not  on  the  average  exceeded  2  or  3  inches.  In  some  cases  bosses  of  the 
harder  conglomerate  which  have  had  no  other  protection  than  a  coating  of 
lichens  and  the  thin  layer  of  detritus  which  they  gather  on  a  steep  slope, 
still  retain  the  deeper  groovings  which  the  ice  impressed  on  them.  So  far 
as  the  bed  rocks  are  concerned,  the  removal  of  matter  from  this  region  since 
the  close  of  the  last  Glacial  period  has  been  entirely  unimportant,  and  the 
decay,  such  as  has  penetrated  so  deeply  in  the  Southern  States,  has  hardly 
begun  even  in  the  most  advantageous  situations  for  the  process.  These 
facts  point  to  the  conclusion  that  the  period  which  has  elapsed  since  the  ice 
left  this  district  has  been,  in  a  geologic  sense,  very  brief 

It  is  to  be  noted  that  the  channels  in  which  the  main  arms  of  Narra- 
gansett  Bay  lie  are  still  rather  deep,  though  their  bottoms  are  probably 
covered  by  a  considerable  thickness  of  drift  materials,  both  that  which  was 
originally  deposited  when  the  ice  was  retreating  and  that  which  has  been 
swept  to  its  place  by  tidal  action.  The  question  suggests  itself  as  to  what 
extent  these  depressions  are  due  to  the  direct  cutting  action  of  the  ice  and 
what  to  the  concomitant  action  of  the  subglacial  streams.  While  it  must  be 
admitted  that  the  general  distribution  of  the  channels  of  the  bay  and  their 
relation  to  the  river  channels  connected  therewith  favor  the  supposition 
that  the  arrangement  of  the  valleys  is  in  the  main  the  result  of  ordinary 
river  action,  it  can  not  well  be  denied  that  the  glacial  work  greatly  changed 
the  forms  and  in  a  measure  the  distributions  of  these  depressions.  Thus 
the  several  rocky  islands  of  the  bay,  with  deep  water  between  them,  can 
not  well  be  explained  by  the  supposition  that  they  are  the  remains  of 
divides  which  once  separated  adjacent  parallel  river  valleys.  The  channel 
between  Bristol  Neck  and  the  north  end  of  'Aquidneck  Island  appears  to 
be  inexplicable  on  the  theory  of  a  submergence  of  river  topography,  but 
it  may  be  accounted  for  on  the  assumption  that  it  is  due  to  glacial  scouring. 


74  GEOLOGY  OF  THE  NARRAGANSETT  BASIN. 

It  is  to  be  noted  that  the  general  form  of  the  basin  is  such  that  the  ice 
during  the  period  when  its  front  lay  beyond  the  present  shore  line  of  the 
continent,  as  it  probably  did  for  the  greater  part  of  the  time  in  which  it 
occupied  this  part  of  the  country,  was  led  somewhat  to  concentrate  its 
flow  in  the  relatively  narrow  space  occupied  by  the  seaward  part  of  the 
basin.  This  concentration  must  have  increased  the  speed  of  the  move- 
ment and  thereby  the  erosive  effect  of  the  moving  ice.  I  have  elsewhere^ 
endeavored  to  show,  by  clearer  examples  than  are  afforded  by  this  field, 
that  the  effect  of  such  an  increase  of  speed,  due  to  the  crowding  of  ice  into 
a  relatively  naiTOw  way,  is  to  intensify  the  erosive  work  which  the  ice  per- 
forms. It  is  also  clear  that  the  subglacial  streams  which  discharged  into  this 
bay  were  very  large.  Such  streams,  so  long  as  they  flow  beneath  the  ice, 
probably  have  a  far  greater  cutting  power  than  open-air  rivers,  for  the  rea- 
son that  they  move  with  an  energy  in  some  measure  intensified  by  the 
height  of  the  column  of  ice  whence  they  are  derived.  As  the  sheet  may 
well  have  had  a  depth  of  some  thousand  feet,  the  impulse  can  be  accounted 
as  great.  These  subglacial  streams  were  competent  to  urge  forward  over 
level  ground  the  bowlders,  often  several  feet  in  diameter,  which  we  now 
find  embedded  in  the  eskers — masses  which  the  most  vigorous  mountain 
torrent  would  hardly  be  able  to  move.  We  may  therefore  reckon  the  sub- 
glacial streams  as  powerful  agents  of  erosion,  quite  competent  to  deepen 
channels  such  as  the  preglacial  rivers  may  have  formed  or  to  cut  new  ways 
if  the  conditions  compelled  them  to  flow  in  other  courses. 

It  must  be  said  that  the  form  of  Narragansett  Bay  is  not  that  of  a 
characteristic  fiord,  such  as  in  the  regions  farther  to  the  northward  clearly 
attest  the  competency  of  glacial  ice  to  excavate  such  basins.  There  is  no 
trace  of  the  sill  or  rock  barrier  across  the  mouth  of  the  bay,  separating  it 
from  the  sea,  such  as  marks  the  normal  Scandinavian  fiords.  We  may, 
however,  hold  that  while  this  Narragansett  system  of  depressions  is  clearly, 
as  regards  its  general  outlines,  the  product  of  erosion  work  done  before  the 
ice  time,  it  owes  much  of  its  form  to  glacial  processes. 

Before  closing  this  brief  account  of  the  glacial  phenomena  of  the  Nar- 
ragansett district  which  demand  notice  in  this  memoir,  we  may  refer  to  the 
general  form  of  the  surface  of  the  basin  with  reference  to  the  jjossible  effect 

'  The  geology  of  the  island  of  Mount  Desert,  Maine,  by  N.  S.  Shaler:  Eighth  Ann.  Rept.  U.  S.  Geol. 
Survey,  Part  II,  1889,  pp.  1007,  et  seq. 


DECAY  PREOEDIFG  GLACIATION.  75 

of  ice  action  in  shaping  the  area.  The  facts  presented  in  this  report  clearly 
indicate  that  the  bed  rocks  have  been  cast  into  exceedingly  varied  flexnres 
and  faultings.  As  these  disturbances  involved  a  great  thickness  of  strata 
and  were  made  apparently  in  a  geologically  short  period,  the  result  must 
have  been  the  formation  of  mountains  of  high  relief  Yet  these  elevations 
have  been  so  completely  effaced  that,  as  is  shown  in  the  maps,  the  region 
is  now  in  the  state  of  a  great  plain,  the  trifling  differences  of  elevation 
being  due  to  the  action  of  the  rivers  and  the  subglacial  streams.  As  before 
remarked,  the  modern  school  of  geographers  Avould  attribute  this  topographic 
character  to  the  process  of  base-leveling,  by  which,  through  the  atmospheric 
agents  of  erosion,  a  surface,  however  diversified,  tends  inevitably  to  be  low- 
ered to  near  the  level  of  the  sea.  Making  what  seems  to  be  due  allow- 
ance for  the  effect  of  repeated  elevation  in  refreshing  the  work  of  the 
streams  and  thus  promoting  the  degradation  of  a  countfy,  a  cause  which 
most  likely  operated  in  the  West  Appalachians  more  effectively  than  on  this 
seashore,  there  still  seem  to  be  needed  some  agents  to  explain  the  remark- 
able planation  of  the  district  we  are  considering.  It  is  likely  that  glaciation 
has  been  one  of  those  auxiliary  agents.  We  will  now  consider  the  way  in 
which  it  may  have  operated  to  bring  planation  about. 

The  evidence  has  been  noted  which  goes  to  show  that  the  rocks  of  this 
basin  were  deeply  decayed  at  the  time  the  work  of  the  last  Glacial  period 
began.  Acting  on  such  a  surface,  the  ice  would  quickly  become  burdened 
with  an  excess  of  ddbris,in  which  state  it  would  resemble  an  ordinary  stream 
of  water  which  has  a  charge  of  sediments  much  greater  than  it  can  carry. 
In  this  case  both  the  fluid  and  the  viscous  streams  necessarily  tend  to 
deposit  a  part  of  their  burden  and  to  flow  over  the  accumulations,  being 
thus  in  part  excluded  from  contact  with  the  bed  rock.  The  deposits  of  the 
overburden  would  naturally  take  place  in  the  valleys,  the  floors  of  which, 
except  when  attacked  by  the  subglacial  streams,  would  remain  uneroded, 
while  the  higher-lying  parts  of  the  field  would  be  cut  away.  As  the  process 
of  erosion  advanced  and  the  waste  from  the  elevated  places  became  smaller 
in  quantity,  the  glacier  would  be  free  to  attack  the  lower  levels.  The  result 
of  this  succession  of  events  would  be  to  level  off  the  inequalities  of  a  country 
which,  owing  to  the  decayed  state  of  the  rocks  at  the  time  the  ice  came 
upon  it,  afi"orded  detritus  more  rapidly  than  the  machinery  of  transporta- 
tion could  bear  it  away.     It  may  be  remarked  that  the  apparently  excessive 


76  GEOLOGY  OF  THE  NAERAGANSETT  BASIN. 

degradation  of  Iron  Hill,  as  above  noted,  can  be  explained  in  this  way. 
It  therefore  seems  reasonable  to  adduce  ice  work  as  one  of  the  agents  which 
have  served  to  bring  about  the  destruction  of  the  original  to^^ographic  reliefs 
of  this  district. 

Along  with  base-leveling  and  ice  work,  there  is  another  class  of  agents 
which  have  doubtless  operated  with  much  effect  in  bringing  the  district  into 
its  planed-down  state.  These  are  the  forces  which  act  at  and  below  the 
level  of  the  sea.  There  can  be  no  question  that  the  effect  of  the  surf  and 
the  shore  currents  is  to  plane  off  the  rocks  and  to  bring  about  such  topo- 
graphic conditions  as  are  found  in  this  basin.  The  only  doubt  is  as  to  the 
rate  at  which  the  work  may  go  on.  Judging  by  the  speed  with  which  the 
benching  action  of  the  sea  proceeds  where  the  attack  is  delivered  on  hard 
(i.  e.,  undecayed)  rocks,  geologists  have  generally  assumed  that  the  aggre- 
gate work  which  is  due  to  this  action  is  relatively  small,  that  it  plays  no 
important  part  as  compared  with  base-leveling  due  to  atmospheric  agents. 
We  must  remember,  however,  that  what  we  know  of  the  extent  of  super- 
ficial decay  in  this  and  other  countries  requires  us  to  believe  that  in  the 
oscillations  of  the  continents  it  must  often  happen  that  deep  sections  of 
rocks  which  have  been  made  very  friable  are  exposed  to  the  mill  of  the  surf 
In  this  case  it  is  fair  to  presume  that  they  might  be  swe^jt  away  with  some- 
thing like  the  speed  which  is  exhibited  in  the  disintegration  of  the  Pliocene 
cliffs  of  Marthas  Vineyard.  When  they  face  the  open  sea,  these  deposits, 
in  coherence  comparable  to  the  decayed  beds  of  the  Southern  Appalachians, 
are  retreating  at  the  rate  of  about  3  feet  per  annum,  as  determined  by 
fifty  years'  observations.  At  this  rate  the  surf  mill  would  be  able  to 
work  inward  across  the  field  of  the  Narragansett  Basin  in  less  than  one 
hundred  thousand  years. 


CHAPTER lY. 

ECONOMIC  RESOURCES  OF  THE  BASIN. 

The  economic  resources  of  the  basin  inchide  the  soils,  the  pottery 
clays,  a  limited  range  of  bnilding  stones,  certain  iron  ores,  and  the  coal 
beds  of  the  Carboniferous  series. 

SOILS. 

The  soils  of  this  region,  being  in  the  main  of  glacial  origin,  have  the 
economic  stamp  of  deposits  which  are  more  or  less  directly  related  to  the 
ice  work.  When,  as  is  the  case  in  the  greater  part  of  the  district  which  lies 
at  more  than  50  feet  above  the  sea,  as  well  as  in  much  of  the  lower  ground, 
the  soil  rests  upon  bowlder  clay,  its  fertility  depends  to  a  great  extent  on 
the  nature  of  the  subjacent  rock.  If  this  be  conglomerate,  as  is  the  case 
over  a  large  part  of  the  central  portion  of  the  basin,  the  soil,  because  of  the 
generally  insoluble  nature  of  the  detritus  from  these  beds,  is  character- 
istically lean.  When  it  rests  upon  sandstones  it  is  of  moderate  fertility. 
Where,  as  in  the  region  about  Newport,  and  generally  on  Aquidneck 
Island,  the  underlying  rock  is  of  shale,  the  soil  is  of  more  than  usual  value. 
The  considerable  organic  matter  of  these  beds  apparently  serves  to  make  a 
richer  field  for  the  plants. 

As  compared  with  other  portions  of  New  England,  this  basin  abounds 
in  glacial  sand  plains.  These  occupy  the  larger  part  of  the  surface  below 
the  level  of  50  feet  above  the  sea,  and  a  considerable  area  of  higher-lying 
ground.  The  relatively  great  extent  of  these  plains  seems  to  be  due  to  the 
fact  that  the  existence  of  the  extensive  depression  of  the  Narragansett  Bay 
made  it  the  point  of  discharge  of  streams  collected  beneath  the  glacier, 
which  bore  great  quantities  of  debris  beyond  the  retreating  ice  front  and 
deposited  the  sandy  portion  of  this  detritus  in  the  shallow  water  of  the  sea, 
which  then  covered  the  area.  These  sand  plains  are  composed  mainly  of 
siUceous  materials,  and  afiford  infertile  soils.     They  are,  however,  of  a  quick 


78  GEOLOGY  OF  THE  NARRAGANSBTT  BASIN. 

nature,  responding  at  once  to  manuring.  Moreover,  they  are  readily, 
though  temporarily,  much  improved  by  plowing  in  green  crops,  the  store 
of  vegetable  matter  thus  introduced  into  the  earth  serving  to  promote  the 
solution  of  the  feldspar,  mica,  etc.,  which  exist  in  the  mass,  though  the  quan- 
tity is  not  considerable.  These  sand-plain  soils,  because  of  the  absence  of 
bowlders,  are  easily  tilled;  they  can  at  certain  points  be  readily  irrigated; 
and  they  thus  are  likely  in  the  modern  time  of  intensive  agriculture  to  be 
valued  more  highly  than  heretofore. 

The  inundated  lands  of  this  district  include  a  small  area  of  marine 
marshes  and  a  considerable  extent  of  fresh-water  swamps.  On  account  of 
the  limited  range  of  the  tides  along  this  part  of  the  coast,  the  reclamation 
of  the  marshes  can  not  be  easily  effected  by  diking.  These  areas  will 
therefore  not  receive  further  consideration.  The  fresh-water  swamps, 
including  in  this  group  all  the  lands  which  are  made  untillable  by  tempo- 
rary flooding  in  the  planting  season,  occupy  an  aggregate  area  of  about 
45  square  miles,  or  nearly  28,000  acres.  The  larger  part  of  this  swamp 
area  is  to  a  greater  or  less  extent  used  as  a  source  of  water  supply  for 
mills,  the  waste  of  the  flood  times  being  there  stored  for  use  in  droughts. 
Until  this  use  of  the  swamps  is  abandoned  it  will  not  be  possible  to  win 
any  large  portion  of  these  over-watered  soils  to  agricultural  use.  About 
one-third  of  the  total  area  consists  of  bogs  of  limited  extent,  which  do  not 
serve  as  reservoirs  and  are  therefore  open  to  improvement.  In  most 
instances  these  fields  can  be  readily  drained  by  means  of  inexpensive 
ditches.  When  so  unwatered,  the  areas  afford  soils  of  two  distinct  groups. 
Around  the  margins  of  each  area  there  is  normally  a  belt  where  the  peaty 
matter  has  not  accumulated  to  a  thickness  of  more  than  a  foot,  and  where, 
after  being  allowed  to  dry,  and  consequently  to  shrink,  it  can,  by  deep 
plowing,  be  incorporated  into  the  soil.  In  these  portions  of  the  drained 
swamps  tillable  fields  of  very  superior  quality  may  be  obtained.  Within 
the  area  of  the  basin  there  is  probably  a  total  extent  of  not  less  than  6,000 
acres  that  is  thus  available  for  agriculture.  Such  ground  is  remarkably 
well  adapted  to  market  gardening.  When  the  peat  of  a  drained  bog  much 
exceeds  a  foot  in  thickness,  it  is  difficult  to  reduce  the  area  to  ordinary  tillage. 
The  only  effective  way  of  accomplishing  this  result  is  by  securing  condi- 
tions of  exceeding  dryness  by  extensive  ditchings,  after  which  the  peat  may 
be  burned,  as  is  done  in  northern  Europe.     In  the  present  condition  of  our 


COAL  BEDS.  79 

agriculture  this  method  may  be  deemed  inapplicable.  Therefore  the  only 
use  which  can  be  made  of  these  bogs  is  for  plantations  of  cranberries.  In 
the  method  of  cultivation  which  is  commonly  employed  with  that  plant, 
several  thousand  acres  of  these  drainable  lands,  especially  the  areas  in  the 
eastern  parts  of  the  basin,  are  well  fitted  to  this  mode  of  tillage. 

COALS. 

The  coal  beds  of  the  Carboniferous  series  afford  the  most  important 
economic  resources  of  the  basin.  As  is  indicated  in  the  portions  of  this 
memoir  which  have  been  prepared  by  Messrs.  Foerste  and  Woodworth, 
these  beds  are  probably  limited  to  the  lower  half  or  shale-bearing  portions 
of  the  great  section.  So  far  as  is  known,  no  deposits  of  any  importance 
exist  in  the  zone  of  the  upper  conglomerates.  The  exhibition  of  these  coals 
is  the  clearest  in  the  region  where  they  have  been  most  extensively  mined, 
on  the  western  side  of  the  northern  part  of  Aquidneck  Island.  At  this  point 
they  are  seen  dipping  to  the  eastward  near  the  surface  at  an  average  angle 
of  about  30°,  with  a  diminishing  slope  as  the  workings  penetrate  toward 
the  center  of  the  syncline.  In  this  section  at  least  two  coal  beds  occur,  the 
lowest  of  which  is  about  2,000  feet  below  the  base  of  the  upper  conglom- 
erates, and  the  highest  within  perhaps  1,000  feet  of  that  line. 

In  the  western  and  northern  parts  of  the  basin  the  same  or  other  coal 
beds  occur.  Of  these,  the  de230sits  in  or  near  Pawtucket  and  at  Cranston 
are  the  best  known.  The  bed  at  Pawtucket — there  seems  to  be  but  one — 
lies  apparently  several  thousand  feet  farther  down  in  the  great  section  than 
the  beds  of  Aquidneck.  It  is  likely  that  this  bed  is  continued  southwardly 
near  the  margin  of  the  basin  to  near  its  southern  end,  and  that  the  various 
exposures  which  have  from  time  to  time  been  made  along  this  line  lie  upon 
it.  It  is  also  probable  that  the  coal  along  the  northern  part  of  that  border, 
as  far  as  Wrentham,  is  of  the  same  or  a  closely  related  stratum. 

The  bed  of  coal  in  Cranston  may  most  reasonably  be  regarded  as 
equivalent  to  one  of  those  in  the  Aquidneck  section.  Its  position  in  relation 
to  the  upper  conglomerates,  however,  can  not  be  ascertained  with  any 
certainty;  so  its  place  must  be  left  in  doubt. 

The  coal  beds  which  were  at  one  time  worked  in  Mansfield  are  in  such 
a  position  that  they  can  not  be  safely  placed  in  reference  to  the  other  known 
deposits.     The  relation  of  the  beds  to  one  another  and  to  the  immediate 


30  GEOLOGY  OF  THE  ^^ARRAGANSETT  HASIN. 

section  in  which  they  lie  inclines  the  observer  to  the  opinion  that  they  are 
the  equivalents  of  the  uppermost  at. the  mines  on  Aquidneck  Island;  but 
this  opinion  has  little  evidence  to  support  it. 

Many  other  deposits  of  coal  have  been  occasionally  exposed  in  various 
parts  of  the  field  in  which  the  carbonaceous  strata  occur.  Some  of  these, 
as,  for  instance,  the  beds  at  Bristol,  have  been  made  the  objects  of  experi- 
mental mining.  The  last-named  deposit  is,  from  its  position,  to  be  reckoned 
in  the  group  occurring  in  the  northern  part  of  Aquidneck,  but  the  greater 
part  of  these  little-known  occurrences  can  only  be  placed  as  below  the 
upper  conglomerate. 

CONDITION   OF  BEDS. 

As  none  of  the  coal  beds  of  this  district  have  been  worked  for  many 
years,  the  accounts  of  the  deposits  can  not  be  made  anew.  The  writer  has 
seen  the  bed  which  was  last  worked  at  the  Aquidneck  mines,  and  also  that 
at  Valley  Falls,  which  to  within  a  few  years  ago  was  mined  for  "foundry 
facino-s,"  and  also  that  which  was  in  a  small  way  exploited  at  Cranston  in 
an  unavailing  effort  to  market  it  as  fuel.  From  these  observations  and 
the  imperfect  records  which  exist  of  the  facts  concerning  the  other  deposits, 
the  following  statements  may  be  made  as  to  the  physical  conditions  of  the 
deposits. 

The  coal  beds  of  this  area  probably  number  a  half  dozen  or  more,  of 
which  only  those  of  the  Aquidneck  group  have  been  proved  to  have  much 
continuity.  Owing  to  a  feature  which,  so  far  as  observed,  they  all  present, 
the  thickness  of  none  of  these  beds  can  be  accurately  determined.  This 
feature  is  the  peculiar  "rolling"  to  which  the  carbonaceous  material  has 
been  subjected  in  the  dislocation  of  the  beds  of  which  it  forms  a  part.  In 
practically  all  cases  the  beds  above  the  coal  have  been  by  the  process  of 
metamorphism  brought  into  a  very  compact  and  rigid  state.  This  change 
appears  to  have  taken  place  before  or  during  the  development  of  the  folds 
into  which  they  have  been  cast.  As  the  process  of  dislocation  went  on,  the 
irregular  strains  acting  on  the  relatively  little  resisting  coal  caused  it  to 
creep  toward  the  points  of  least  pressure.  Tlae  result  was  that  wherever 
the  bed  has  been  followed  in  the  direction  of  the  dip  for  a  considerable 
distance  the  layer  is  found  to  widen  and  contract,  so  that  in  a  variable  length 


POSITION  AND  EXTENT  OP  COAL  BEDS.  81 

of  from  a  few  score  to  600  or  800  feet  it  may  pass  from  a  mere  trace  to  the 
thickness  of  20  feet  or  more,  the  cross  section  having  a  rudely  lenticular 
form.  Followed  horizontally,  these  thick  portions  of  the  vein  thin  toward 
either  end — at  least  that  is  the  impression  made  by  a  study  of  the  Ports- 
mouth mine.  So  far  as  could  be  seen  there,  the  horizontal  dimension  of  the 
lens  was  much  greater  than  that  shown  in  descending  the  slope.  It  is 
evident  that  these  conditions  exclude  any  careful  study  as  to  the  thickness 
of  the  beds.  It  may  be  said  that  a  rough  computation  of  the  contents  of 
the  principal  bed  mined  at  Portsmouth  showed  it  to  be  probable  that  the 
thickness  of  the  deposit  before  it  was  disturbed  by  the  shearing  action  was 
not  far  from  4i]  feet. 

It  need  not  be  said  that  this  irregular  form  of  the  coal  deposits,  com- 
bined, as  it  is,  with  a  certain  amount  of  faulting,  which,  though  not  dis- 
tinctly shown  in  the  small  workings,  is  evident  in  the  structure  of  the  field, 
makes  it  important  to  determine  how  far  these  features  are  general  through- 
out the  basin.  On  this  point  the  information  is  very  scanty.  It  may  be 
said,  however,  that  where,  as  in  the  Portsmouth  mine,  the  workings  had  gone 
for  a  distance  of  about  1,400  feet  from  the  outcrop,  and  where  the  steepness 
and  the  dip  considerably  lessened  with  the  approach  to  the  center  of  the 
syncline,  the  irregularity  of  the  bed  had  perceptibly  diminished,  giving 
some  reason  to  expect  that  there  was  an  extensive  area  of  coal  in  that  cen- 
tral part  of  the  trough  which  had  not  been  much  dislocated.  Unfortunately, 
this  is  the  only  portion  of  the  basin  whei'e  there  is  sufficient  basis  for  reck- 
oning that  the  coals  within  reach  of  mining  work  occupy  a  position  which 
gives  them  the  chance  of  escaping  the  effects  of  "rolling-." 

Owing  to  the  lack  of  detailed  knowledge  concerning  the  position  of 
the  coals,  or  even  of  the  precise  attitude  of  the  rocks  in  this  basin,  it  is  not 
yet  possible  to  estimate  with  any  approach  to  accuracy  the  area  in  which 
coals  of  workable  thickness  may  be  found.  It  may  be  said  in  general  that 
all  parts  of  the  section  lying  more  than  2,000  feet  below  the  base  of  the 
upper  conglomerates  show,  from  point  to  point,  traces  of  coal.  Consid- 
ering the  numbers  of  these  chance  ex^iosures,  and  noting  the  general  way 
in  which  the  portions  of  the  section  containing  coal  are  hidden  by  glacial 
detritus,  there  is  reason  to  believe  that  a  considerable  part  of  the  rocks 
below  the  indicated  level   are    in   some  measure   coal  bearing.     Definite 

MON  XXXIII 6 


82  GEOLOGY  OF  THE  ISIAERAGANSETT  BASIN. 

information  as  to  the  extent  and  thickness  of  these  beds  can  not  be  had 
without  extensive  and  systematic  exploration  with  the  drill,  but  some  results 
could  be  obtained  by  well-planned  superficial  excavations. 

It  should  be  noted  that,  owing  to  the  thickness  of  the  barren  upper 
part  of  the  section  of  the  rocks  in  the  basin,  nearly  one-fourth  of  its  area 
has  the  coal-bearing  beds  so  deeply  buried  that  they  are  below  the  level 
where  they  could  be  mined;  in  much  of  the  area  the  estimated  depth 
exceeds  10,000  feet.  Moreover,  nearly  another  fourth  of  this  area  is  occu- 
pied by  the  waters  of  the  sea,  so  that  it  may  be  regarded  as  impracticable 
to  explore  the  underlying  rocks.  The  remaining  half  is  fairly  open  to 
inquiry  provided  there  should  be  found  a  market  for  coal  of  the  peculiar 
qi;ality  which  it  affords,  at  a  cost  which  would  be  imposed  by  its  physical 
and  chemical  conditions.     These  we  will  now  note: 

CHARACTERISTICS    OF    THE    COALS. 

Wherever  found,  the  coal  of  this  basin  has  certain  characteristics  which 
distinctly  separate  it  from  any  other  fossil  fuel  that  has  been  mined  in 
this  country.  The  material  is  everywhere  extremely  anthracitic,  often 
ranging  in  appearance  toward  graphite.  It  is  usually  much  penetrated  by 
veins  of  varied  and  rather  complicated  nature.  It  is  high  in  ash,  the  pro- 
portion commonly  being  10  per  cent,  and  often  attaining  to  near  twice  that 
amount.  This  ash  contains  in  most  instances  a  singularly  large  amount  of 
lime,  which  causes  the  cinders  to  smelt  and  thus  clog  the  grate  bars  of  a 
stove  or  boiler  furnace.  As  is  shown  by  the  accompanying  analysis,  the 
percentage  of  fixed  carbon  is  abnormally  high,  yet  an  extended  trial  of  the 
coal  in  producing  steam  showed  that  the  value  for  this  purpose  was  but  72 
per  cent  of  that  of  Lackawanna  coal.  The  reason  for  this  disproportion 
may  have  been  in  part  the  lack  of  adaptation  of  the  fire  boxes  to  the 
character  of  the  fuel,  which  evidently  needs  a  very  strong  draft,  and  the 
fusible  nature  of  the  slag,  which  makes  it  difficult  to  keep  the  grate  bars 
clean.  It  is  possible,  however,  that  a  portion  of  the  carbon  is  in  some 
special  chemical  state  which  hinders  its  ready  combination  with  oxygen, 
perhaps  in  the  condition  of  the  supposed  graphitic  acid  of  Graham. 


COAL  ANALYSES. 


83 


Annli/ses  of  coal  from  the  Portsmouth  mine,  Portsmouth,  Rhode  Island.' 
[Analysts,  Dr.  F.  A.  Gooeh  and  Mr.  B.  T.  Putnam.] 


I. 

II. 

III. 

IT. 

V. 

VI. 

vn. 

VIII. 

IX. 

Water 

5.12 

6.49 

71.04 

17.35 

0.52 
6.31 
76.23 
16.94 

3.18 

4.43 
75.97 
16.42 

2.25 
6.46 
79.59 
11.70 

7.62 
5.42 
74.40 
12.56 

7.96 

4.95 

76.22 

10.87 

8.76 

7.23 

70.24 

13.77 

10.27 
5.99 
67.50 
16.24 

10.47 
5.83 
66.95 
17.05 

Volatile  combustible  . . . 

Carbon  

Ash             . .              

Sulphur 

Ash 

100.  CO 
0.216 
Red. 

10.94 

100.  00 
0.224 
Red. 

12.08 

100. 00 
0.258 
Eed. 

17.14 

100. 00 
0.643 
Red. 

12.32 

100.  00 
0.28 

13.72 

100.  00 

100.  00 

100.  00 

100.  00 

Red. 
15.39 

Red. 
9.71 

-'^^l-*Kv3?Sib.)- 

11.26 

11.48 

I.  Bottom  of  shaft,  north  side;  thickness  of  seam,  3  feet  11  inches. 
II.  Bottom  of  shaft,  south  side ;  thickness  of  seam,  2  feet  7  inches. 

III.  South  side,  50  feet  from  bottom;  thickness  of  seam,  6  feet. 

IV.  South  gallery,  370  feet  from  bottom;  upper  three-fourths  of  6-foot  seam. 

(Analyses  I,  II,  III,  and  IV  are  from  samples  taken  across  the  Tvidth  of  the  seam.) 
V.  The  average  of  seven  analyses  made  from  samples  taken  at  intervals  along  the  length  of  a 

6-foot  drill  core,  cut  out  of  what  is  known  as  the  "back  seam,"  at  about  90  feet  below  the 

mouth  of  the  Portsmouth  mine. 
VI  and  VII.  The  single  analyses  of  this  series  showing  the  maximum  and  minimum  percentages  of 

carb(m  and  ash. 
VIII  and  IX.  Samples  taken  from  two  lots,  of  several  tons  each,  of  freshly  mined  coal  used  in  other 

experiments. 

Although  it  is  probable  that  if  the  coal  can  be  rained  in  the  undisturbed 
central  parts  of  the  shallower  synclines  it  will  there  be  found  to  contain  less 
vein  matter,  and  hence  will  be  lower  in  ash,  its  high  percentage  of  the  latter 
and  its  other  objectionable  peculiarities  may  have  to  be  reckoned  as  insu- 
perable. It  is  therefore  very  doubtful  whether  it  can  ever  be  brought  into 
service  for  ordinary  uses.  The  experiments  heretofore  referred  to  appear 
to  show  that  it  can  not  be  given  a  fair  place  for  steaming  purposes.  The 
fact  that  while  the  Portsmouth  mine  was  working,  the  people  of  the  neigh- 
borhood were  not  willing  to  pay  more  than  two-thirds  of  the  cost  of  Penn- 
sylvania anthracite  for  its  product,  shows  that  it  is  not  well  suited  for  house- 
hold use.  There  remain,  however,  as  before  remarked,  certain  fields  in 
which  this  fuel  may  well  find  a  jDlace.  These  are  ore  smelting,  the  manu- 
facture of  water  gas,  and  the  process  of  burning  brick  when  the  powdered 
coal  is  placed  between  the  layei's  of  the  kiln. 

'  Notes  on  the  Rhode  Island  and  Massachusetts  coals,  by  A.  B.  Emmons :  Trans.  Am.  Inst.  Min. 
Eng.,  Vol.  XIII,  1885,  p.  511. 


84  GEOLOGY  OF  THE  NAERAGANSETT  BASIN. 

As  to  the  first  of  the  aforenamed  uses,  it  may  be  said  that  the  coal 
of  this  basin  seems  to  be  fairly  well  suited  to  the  needs  of  smelting. 
It  is  low  in  sulphur;  its  specific  gravity  is  so  high  that  it  will  give  a 
large  number  of  heat  units  for  a  given  bulk;  the  ash,  though  high,  is, 
owing  to  its  composition,  easily  smelted.  I  was  told  by  the  person  who 
owned  the  mine  at  Portsmouth  the  greater  part  of  the  time  during  which 
it  was  worked,  that  the  coal  was  the  best  that  could  be  obtained  for 
smelting  copper  ores  as  well  as  for  the  subsequent  working  of  that  metal. 
The  further  statement  was  made  that  a  cargo  of  the  fuel  had  been  sent  to 
an  iron  furnace  on  the  Hudson  and  that  it  proved  very  satisfactory  as  com- 
pared with  the  anthracite  of  Pennsylvania  in  making"  Bessemer  pig.  I  was 
also  informed  by  one  of  the  Crocker  Brothers  of  Taunton,  Massachusetts, 
who  worked  the  mine,  that  a  test  of  a  few  tons  of  the  coal  had  been  made 
in  the  manufacture  of  water  gas  and  that  it  was  well  suited  to  the  purpose. 
It  is  not  now  possible  to  verify  these  statements,  but  they  appear  to  be  quite 
consistent  with  what  is  known  of  the  nature  of  the  anthracite  of  this  field. 

The  only  imdetermined  qualification  of  the  Narragansett  coals  as 
regards  their  use  in  the  special  arts  above  mentioned  is  that  observed  by 
Dr.  Arthur  B.  Emmons  and  described  in  the  paper  referred  to.  This,  in 
the  words  of  the  author,  is  "  the  striking  peculiarity  (hitherto  unnoticed  in 
anthracite  coals,  or,  I  believe,  in  any  coals)  of  quickly  taking  up  a  large  per- 
centage of  water  under  a  moist  condition  of  the  atmosphere  and  as  readily 
parting  with  it  under  a  drier  condition  of  the  atmosphere."  According  to  the 
records  obtained  by  Dr.  Emmons  and  his  collaborator,  Dr.  F.  A.  Gooch,  the 
Narragansett  coal  may,  with  the  changes  in  the  humidity  of  the  air,  vary  as 
much  as  15  per  cent  of  the  whole  weight  of  the  material.  How  far  this 
peculiarity  may  affect  the  value  of  the  coal  in  the  smelter  or  water-gas 
converter  will  have  to  be  determined  in  an  experimental  way. 

In  considering  the  prospective  value  of  this  coal,  the  cost  of  mining  it 
is  of  course  a  matter  of  much  importance.  So  far  the  practical  experiments 
in  mining  have  been  too  few  and  too  imperfectly  executed  to  afford  any 
clear  determination.  The  mine  at  Portsmouth,  the  only  one  in  the  basin 
maintained  in  operation  for  any  considerable  time,  was  not  well  managed. 
As  the  deep  part  of  the  pit  was  almost  absolutely  dry,  the  little  water  found 
in  it  entering  from  the  old  upper  workings,  there  was  but  slight  expense  for 
pumping,  the  drip  collected  in  the  sump  being  hauled  about  once  a  month 


EXPLORATION  FOR  COAL.  85 

in  one  car.  The  roofs  of  the  seam  were  admirably  strong,  requiring  practi- 
cally no  timbering  even  where  the  pillars  were  robbed  to  a  very  extreme 
point.  At  the  time  1  last  examined  the  place  the  best  information  which 
could  be  had  indicated  that  the  cost  of  lifting  the  coal  and  treating  it  at  the 
breaker  amounted  to  about  $2.50  a  ton.  An  estimate  based  on  a  suitable 
amount  of  surface  plant  and  proper  approaches  to  the  vein,  with  a  fit  admin- 
istration, indicated  that  at  the  present  price  of  labor  the  coal  could  be  mined, 
so  long  as  the  bed  was  in  the  then  existing  favorable  position,  for  about  one- 
half  the  sum  it  was  then  costing.  If  the  coal  is  found  as  a  little-distorted 
bed,  averaging  say  4  feet  thick  over  as  much  as  3  square  miles  in  the  cen- 
tral part  of  the  basin,  it  should  by  means  of  vertical  shafts  be  possible  to 
mine  it  at  a  yet  lowej"  cost  than  that  named. 

CONDITIONS  OF  FUTURE  ECONOMIC  WORK. 

As  to  the  best  places  for  future  exploration,  it  may  be  said  that  it 
seems  to  be  undesirable  to  undertake  any  further  search  for  the  coal  at  the 
outcrops,  the  presumption  and  the  evidence  being  alike  in  favor  of  the 
opinion  that  at  such  places  the  coal,  lying  at  a  steep  dip,  is  more  likely  to 
be  much  infiltered  with  vein  matter.  The  aim  should  be  to  seek  the  beds 
in  the  central  parts  of  the  synclines,  or  where,  though  monoclinal,  the  strata 
have  a  low  dip. 

The  best  of  these  places  appears  to  be  that  in  the  northern  part  of  Aquid- 
neck  Island.  If  the  apparent  diminution  in  the  slope  of  the  strata  toward 
the  center  of  this  trough  be  verified,  there  is  a  reason,  before  remarked,  to 
expect  a  considerable  area  of  the  coal  beds  in  the  central  part  of  the  north- 
ern end  of  the  island,  where  the  rocks  seem  a  little  disturbed.  There  is  no 
very  clear  evidence  as  to  the  depth  below  the  surface  at  which  the  coal  may 
li,e,  but  it  seems  quite  probable  that  this  depth  is  less  than  1,800  feet  in  the 
central  portion  of  the  area.  To  determine  the  true  position  of  the  deposits, 
a  line  of  borings  should  be  carried  across  this  part  of  Aquidneck  Island  in 
a  nearly  east-west  direction,  with  its  western  end  about  600  feet  from  the 
vertical  plane  where  the  old  workings  stopped.  It  will  be  well  to  supple- 
ment the  information  thus  gained,  especially  if  the  indications  so  obtained 
are  favorable,  by  other  borings  carried  southward  toward  Quaker  Hill. 

The  next  most  promising  field  for  exploration  is  the  belt  of  country 
lying  immediately  to  the  east  of  the  northward  extension  of  the  Providence 


86  GEOLOGY  OF  THE  NARRAGANSETT  BASIN. 

River,  where,  if  the  determinations  of  the  sti'ucture  as  set  forth  in  this 
report  are  correct,  the  equivalents  of  the  Portsmouth  coal  beds  should  be 
found.  The  known  facts  go  to  show  that  in  this  part  of  the  field  the  rocks 
are  not  much  disturbed,  and  that  these  coal  beds  are  in  the  place  where  it 
is  supposed  they  should  occur.  Should  these  suppositions  be  verified, 
there  may  be  an  area  of  20  or  more  square  miles  in  which  the  conditions 
are  favorable  for  mining  operations.  In  connection  with  this  part  of  the 
field,  it  is  necessary  to  set  forth  the  facts  concerning  a  boring  made  in  the 
town  of  Seekonk  about  twenty-five  years  ago.  This  gave  a  section  of 
the  rocks  which  at  its  base  appeared  to  indicate  the  occurrence  of  a  bed 
of  fairly  good  anthracite  at  a  depth  of  about  700  feet  below  the  surface  of 
the  ground.  There  can  be  no  doubt  as  to  the  fact  that  the  boring  was 
made.  Abundant  samples  of  the  core  were  examined  by  the  writer  about 
five  years  after  the  work  was  done.  They  were  then  in  the  possession  of 
the  man  on  whose  land  the  boring  was  made.  They  showed  the  rocks  to 
be  of  the  general  character  of  those  which  overlie  the  Portsmouth  beds,  and 
also  that  the  beds  are  not  very  much  disturbed,  the  dip  averaging  not  more 
than  20°,  probably  to  the  eastward.  An  analysis  of  the  coal  showed  it  to 
have  the  general  character  of  the  Rhode  Island  deposits,  being  extremely 
anthracitic.  Mr.  Emmons,  in  the  paper  above  referred  to,  states  that,  while 
the  boring  down  to  the  level  of  the  coal  is  the  result  of  an  honest  inquiry, 
the  coal  is  a  fiction,  the  portion  of  the  core  showing  the  coal  having  been 
made  on  the  ground  by  operating  the  drill  several  times  through  a  large 
lump  of  coal  brought  by  the  disappointed  explorer  to  the  man  who  was 
managing  the  apparatus,  ostensibly  to  find  whether  the  instrument  would 
cut  a  clean  core  in  material  of  that  degree  of  hai-dness.  On  review  of  all 
the  facts,  it  appears  worth  while  to  reopen  this  drill  hole,  which  was  carefully 
plugged  at  the  time  the  work  was  abandoned,  and,  Avith  a  reamer,  to  test 
the  bottom  of  the  opening,  in  order  to  ascertain  the  truth.  If  coal  is  not 
found,  it  will  still  be  well  to  continue  the  drill  work  already  done,  down- 
ward as  far  as  it  may  be  conveniently  possible  to  do  so,  for  the  reason 
that  not  far  below  the  base  of  the  present  opening  we  may  expect  to  pene- 
trate the  portion  of  the  section  where  the  beds  of  the  Portsmouth  district 
belong.  If  the  section  could  be  carried  to  the  depth  of  say  3,000  feet,  the 
information  would  be  of  great  value  as  related  to  the  possibility  of  finding 
workable  coal  in  the  northern  portion  of  tlie  basin. 


EXPLORATION  FOE  COAL.  87 

By  reference  to  the  map  (PI.  XVII)  it  will  be  seen  that  the  upper  con- 
glomerates occupy  an  insular  position  in  the  northern  part  of  the  basin,  in 
which  they  have  been  left  by  the  degradation  of  the  folds  in  which  they  lie. 
So  far  as  has  been  learned,  there  are  no  faults  or  other  local  disturbances 
which  should  make  it  improbable  that  the  beds  equivalent  to  the  Portsmouth 
coal-bearing  part  of  the  section  are  found  in  their  due  place  in  the  belt  of 
country  on  the  north  and  east  of  this  conglomerate  area.  It  is  to  be  noted, 
however,  that  so  far  no  coal  beds  have  been  revealed  in  this  belt  by  natural 
exposure  or  by  chance  excavations ;  but  this  may  be  accounted  for  by  the 
fact  that  the  district  is  much  more  deeply  covered  by  the  drift  mantle  than 
that  to  the  westward  and  northward.  Therefore  this  section,  within  say  a 
mile  of  the  margin  of  the  upper  conglomerates,  may  be  regarded  as  next  in 
promise  to  the  sections  before  mentioned  as  a  field  for  explorations.  It 
should  be  observed  that  the  angle  of  the  dip  toward  the  center  of  the 
Taunton  or  Great  Meadow  Hill  syncline  (see  figs.  8,  9,  in  Part  II  of  this 
monograph,  pp.  122,  123)  makes  it  probable  that  at  a  little  distance  within 
the  margin  of  the  coarse  conglomerates  the  coal  beds  which  would  lie  in 
the  strata  plane  of  those  at  Portsmouth  would  be  greatly  below  the  level 
where  they  could  be  profitably  worked. 

As  yet  no  adequate  information  has  been  attained  which  may  serve  to 
show  the  conditions  of  the  basin  in  the  region  to  the  east  of  the  city  of 
Taunton.  In  that  place  a  boring  carried  to  the  depth  of  850  feet  revealed 
no  good  coal;  indeed,  but  little  more  than  carbonaceous  matter  was  found. 
The  beds  are  presumably  the  equivalent  of  those  which,  in  a  thickness  of 
2,000  feet  or  more,  overlie  the  coals  of  the  Portsmouth  mines.  The  churn 
drill  gave,  of  course,  no  information  as  to  the  attitude  of  the  rocks.  It 
seems  likely  that  there  are  but  slight  faults  or  folds  in  this  part  of  the  field, 
and  that  in  the  main  the  beds  belong  to  the  section  which  may  be  expected 
to  contain  coals. 

For  the  reasons  before  given,  which  go  to  show  that  it  is  not  worth 
while  further  to  explore  for  coal  around  the  margins  of  the  basin,  there 
remains  only  one  other  portion  of  its  area  to  consider.  This  is  the  field 
between  Aquidneck  Island  and  the  western  shore  of  Narragansett  Bay.  The 
greater  part  of  this  district  is  covered  by  water.  All  that  part  of  it  which 
lies  to  the  south  of  the  northern  end  of  Canonicut  Island  is  evidently  so 
affected  by  regional  metamorphism  that  any  coal  which  it  may  contain  is 


88  GEOLOGY  OF  THE  NAEEAGANSETT  BASIN. 

likely  to  be  of  very  poor  quality.  The  water-covered  area  is,  as  before 
noted,  difficult  to  explore.  If,  however,  coal  should  eventually  be  found 
beneath  those  arms  of  the  sea,  it  could  doubtless  be  mined  with  safety, 
though  with  added  cost,  on  accoimt  of  the  difficulties  of  access. 

Before  any  further  costly  effoii  to  develop  the  coal  deposits  of  this  dis- 
trict is  made  the  coal  from  some  one  of  the  openings — that  at  Portsmouth, 
for  instance — should  be  subjected  to  systematic  and  thorough  experiments 
to  determine  its  value  in  the  wide  range  of  arts  to  \vhich  this  fuel  may  be 
applied.  These  tests  should  include  at  least  the  arts  of  ore  smelting  and 
the  manufacture  of  water  gas,  brick,  and  pottery.  Experiments,  which  on 
theoretical  grounds  appear  to  be  very  promising,  should  be  made  in  crush- 
ing and  washing  the  coal  and  in  subsequently  converting  it  into  briquettes. 
It  may  be  found  that  in  this  form  the  material  will  prove  ser^aceable  as  an 
ordinary  fuel.  There  can  be  little  doubt  that  this  inquiry  should  be  under- 
taken. As  before  noted,  there  is  a  very  large  amount  of  coal  in  this  basin, 
although  there  is  no  basis  of  reckoning  the  total  quantity  with  any  approach 
to  accuracy.  There  can  be  little  doubt  that  it  is  to  be  estimated  by  the 
hundred  million  tons.  Even  though,  as  has  been  assumed,  this  coal  can  not 
compete  in  ordinary  uses  with  that  which  is  imported,  the  chance  that  it 
may  serve  in  many  important  arts  affords  full  warrant  for  a  careful  stud}^  of 
its  quality  and  distribution. 

The  inquiry  above  noted  could  be  undertaken  on  a  lesser  scale,  lim- 
iting it  to  the  Portsmouth  field.  As  already  stated,  this  is  a  typical  area, 
probably  the  best  in  the  basin.  Work  there  should  first  be  directed  to 
ascertaining  the  extent,  condition,  and  depth  at  which  the  coals  occur 
in  the  central  portion  of  the  trough  in  which  they  lie.  If  the  results 
obtained  are  satisfying,  it  will  be  easy  to  obtain  from  the  existing  openings 
enough  coal  to  make  the  trials  which  have  been  suggested.  Supposing 
these  tests  to  show  economic  value,  the  old  workings  should  be  abandoned 
and  the  beds  approached  by  means  of  a  vertical  shaft,  so  placed  as  to  enter 
them  as  near  as  possible  to  the  center  of  the  basin. 

IROlSr  ORES. 

The  iron  ores  on  the  western  border  of  the  Narragansett  Basin  have 
a  certain  amount  of  economic  interest,  in  that,  in  case  the  coal  is  ever 
developed,  they  may  become  of  value  for  the  purpose  of  mixing  with  the 


FUEL  FOR  SMELTING.  89 

ore  brought  from  other  parts  of  this  country  or  from  abroad.  The  only 
iron  ore  of  promise  in  this  field  is  that  which  occurs  at  the  eminence  known 
as  Iron  Hill,  which  lies  in  the  town  of  Cumberland,  about  2^  miles  east  from 
Woonsocket,  Rhode  Island.  The  deposit  is  a  rather  ilmenitic  magnetite,^ 
containing  about  35  or  40  per  cent  of  metallic  iron,  but  it  is  remarkably  free 
from  phosphorus,  in  this  regard  closely  resembling  the  best  Swedish  ore, 
which  it  also  resembles  in  its  petrographical  characters.  The  mass  of  the 
ore,  apparently  in  its  nature  a  dike,  runs  along  the  general  surface  of  the 
country  in  which  it  lies,  to  the  height  of  nearly  100  feet.  It  has  a  width 
of  about  600  feet  and  is  of  about  twice  that  length.  It  is  probably  con- 
tinued downward  to  an  indefinite  depth,  and  may  extend  for  a  considerable 
distance  beneatli  the  cover  of  drift  to  the  north  and  south,  in  which  axis 
the  mass  seems  to  trend.  The  mass  of  ore  may  therefore  be  reckoned  as 
large;  it  probably  could  afford,  if  desired,  a  total  of  10,000,000  tons  or  more 
without  particularly  deep  workings  The  limestones  of  Lincoln,  Rhode 
Island,  between  Iron  Hill  and  the  western  margin  of  the  Carboniferous  rocks, 
afford  an  excellent  flux.  As  they  appear  in  the  form  of  white  crystalline 
marble,  it  is  probable  that  they  also  are  nonphosphatic.  Thus,  if  the  coal 
of  the  Narragansett  Basin  proves  to  be  as  useful  as  a  smelting  fuel  as  it 
promises  to  be,  the  shores  of  the  bay  may  prove  to  be  well  equipped  for 
the  manufacture  of  pig  iron. 

About  twenty-five  years  ago  the  coal  from  the  Portsmouth  mines  was  to 
a  certain  extent  used  in  smelting  copper  ore  which  was  mainly  brought  from 
South  America.  It  was  stated  when  this  process  was  in  operation  that  the 
fuel  was  satisfactory.  If  this  was  the  case,  there  is  yet  another  reason  for 
supposing  that  the  coal  of  this  basin  has  a  value  when  used  in  the  reduc- 
tion of  metals.  As  a  whole  the  evidence  thus  points  to  the  conclusion  that 
those  who  undertake  to  bring  these  coals  into  the  market  will  do  well  to 
look  carefully  into  the  question  of  their  adaptation  to  this  use.  If  this 
element  of  value  could  be  verified,  the  basis  for  the  development  of  the 
deposits  might  be  found  without  reference  to  the  other  ends  to  which  their 
product  might  be  applied. 

In  closing  these  remarks  concerning  the  economic  values  of  mines  in  the 
Narragansett  Basin,  it  may  be  said  that,  as  far  as  the  coal  beds  are  concerned, 

'  See  A  microscopical  study  of  the  iron  ore  or  peridotite  of  Iron  Mine  Hill,  Cumberland,  B.  I., 
by  M.  A.  Wadsworth:  Proc.  Boston  Soc.Nat.  Hist.,  Vol.  XXI,  1883,  pp.  194-197. 


90  GEOLOGY  OF  THE  NARRAGANSETT  BASIK 

the  developments  are  not  sufficiently  advanced  to  enable  the  geologist  to 
prove  very  helpful  to  those  who  desire  to  exploit  its  resources.  Such 
indications  as  are  here  given  are  therefore  to  be  regarded  as  suggestions 
rather  than  as  definite  recommendations;  the  latter  can  be  safely  made 
only  when  accurately  determined  facts,  such  as  are  obtained  from  extensive 
workings,  have  been  gathered. 


GEOLOGY  OF  THE  NARRAGANSETT  BASIN 


Part  II.— THE    NORTHERN    AND    EASTERN    PORTIONS 
OF   THE    BASIN 


A  BIBLIOGRAPHY  OF  THE  CAMBRIAN  AND  CARBONIFEROUS 
ROCKS  OF  THE  BASIN 

By   JAY    BA.CKXJS    ^VOOJD^^^ORTH 


CONTENTS. 


Page. 

Chapter  I. — The  problem  of  stratigraphic  succession 99 

Repetition  of  lithologieal  characters 100 

Transition  of  lithologieal  characters 100 

Effects  of  igneous  intrusions 101 

Metaraorphism 101 

Folding  and  faulting 101 

Denudation 101 

Glaciation 102 

Submergence 103 

Absence  of  artificial  excavations 103 

Chapter  II. — The  pre-Carboniferous  rocks 104 

Algonkian  period 104 

Blackstone  series 104 

Cumberland  quartzites 106 

Ashtou  schists 107 

Smithfield  limestones 107 

Cambrian  Period 109 

Lower  Cambrian 109 

Middle  Cambrian  (unrepresented) 109 

Upper  Cambrian 109 

Silurian  Period  (unrepresented) 113 

Chert  pebbles 113 

Chapter  III. — The  igneous  rocks  of  the  border  of  the  basin 114 

Granitic  rocks 114 

Plympton  felsites 116 

Granite-porphyry 117 

Other  rocks 117 

Gabbro  hills  of  Sharon 118 

Chapter  IV. — The  Carboniferous  basin 119 

General  structure  of  the  basin 121 

Maps  of  the  boundary  of  the  basin 124 

Boundary  of  the  basin  on  the  north  and  east 125 

From  Cranston  to  the  Blackstoue  River 125 

From  Blackstone  River  to  Sheldonville 127 

Connection  between  the  Narragansett  and  Norfolk  County  basins 127 

Sheldonville  cross  fault 127 

From  Sheldonville  to  Foolish  Hill 127 

Foolish  Hill  fault 128 

From  Foolish  Hill  to  Brockton 128 

From  Brockton  to  the  North  River 129 

Shumatuscacant  fault 129 

From  North  River  to  Lake ville 129 

From  Lakeville  to  Steep  Brook 130 

Inliers 130 

North  Attleboro  inlier 131 

Nemasket  granitite  area 131 

Summary 131 


94  CONTENTS. 


Chapter  V. — The  Carboniferous  strata 133 

Determination  of  horizons  within  the  basin 133 

Means  of  determining  superposition 133 

Tabular  view  of  the  strata  in  the  Narragansett  Basin 134 

Formations  below  the  Coal  Measures 135 

Pondville  group 135 

Basal  arkose  beds 135 

Foolish  Hill  exposures 135 

North  Attleboro  exposures 135 

Pierces  Pasture  in  Pondville,  Norfolk  County  Basin 135 

Absence  of  basal  granitic  conglomerates 136 

Geographical  conditions  indicated  by  the  basal  arkose 137 

Absence  of  iron  oxides  in  the  basal  arkose 138 

Absence  of  carbonaceous  matter  along  northern  margin 139 

Extent  of  arkose  zone 139 

Suprabasal  conglomerates 140 

Millers  River  conglomerate 140 

South  Attleboro  exposure 140 

Jenks  Park  exposure  in  Pawtucket 141 

Wamsutta  group 141 

Eed  rock  areas 142 

Area  along  the  northern  border 143 

Gray  sandstones  of  the  northern  border 144 

North  Attleboro  area 145 

Conglomerates 146 

Sandstones 147 

Shales 147 

Central  Falls  area 147 

Pawtucket  area 148 

Eed  beds  in  Attleboro,  Eehoboth,  and  Norton 148 

Norfolk  County  area 148 

South  Attleboro  limestone  bed 149 

Attleboro  sandstone 151 

Igneous  associates  of  the  Wamsutta  group 152 

Diabase 152 

Quartz-porphry  group 153 

Diamond  Hill  quartz  mass 155 

Wamsutta  volcanoes 155 

Folding  of  the  Wamsutta  group 156 

Flora  of  the  Wamsutta  group 158 

Coal  Measures 159 

Cranston  beds 159 

Providence  area 159 

Pawtucket  shales 162 

Sockanosset  sandstones 163 

East  Side  area  in  Providence 163 

Tenmile  Eiver  beds 164 

Lebanon  Mills  exposure 164 

East  Providence  area 164 

Leonards  Corner  quarries 165 

Section  from  Watchemocket  Cove  to  Riverside 165 

Halsey  Farm  section  at  Silver  Spring 166 

Exposures  in  Seekonk 168 

Hunts  Mills  section 169 

Perrins  anticline 169 

Bored  well  near  Lebanon  Mills 170 


CONTEJSTS.  95 

Chapter  V. — The  Carboniferous  strata — Continued. 

Coal  Measures — Continued.  Page. 

Seelionlibeds 173 

Seekonk  conglomerate 174 

Beds  north  of  the  Tenmile  River  in  Attleboro , 17.t 

Contact  of  red  and  gray  beds,  with  local  unconformity 176 

Red  shales 177 

Raindrop  imprints 178 

Attleboro  syncline 179 

Blake  Hill  fault  block , 180 

Fossils '. 181 

Coal 182 

Blake  Hill  thrust  plane 183 

Dighton  conglomerate  group 184 

Extension  of  the  Coal  Measures  north  and  east  of  Taunton 187 

Dedham  quadrangle 187 

Mansfield  area 1S8 

Flora  of  Mansfield  section 191 

Bridge  water  area 192 

Abington  quadrangle 193 

Taunton  quadrangle 195 

Red  beds 195 

Outcrops  in  Norton 195 

Winneconnet  ledges 196 

Scolithus  beds 197 

Taunton  waterworks  section 198 

Westville  section 199 

Taunton  River  Valley 200 

Middleboro  quadrangle 200 

Chapter  VI. — Organic  geology 202 

Insect  fauna 202 

Stratigraphic  position  of  the  fauna 203 

Odontopteris  flora 203 

List  of  plants  identified  by  Lesquereux 204 

Coal  beds 205 

Search  for  coal 207 

Thickness  of  the  Carboniferous 208 

Acknowledgments 211 

Appendix. — Bibliography  of  the  Cambrian  and  Carboniferous  rocks  of  the  Narragansett  Basin. .  212 


ILLUSTRATIONS 


Plate         II.  Pre-Carbouiferous  rocks  at  western  border,  near  Providence,  Rhode  Island 12G 

III.  Plant-bearing  outcrop  of  Wamsutta  group  in  North  Attleboro,  Massachusetts 146 

IV.  Faulted  diabase  dikes  in  North  Attleboro,  Massachusetts 152 

V.  Rocky  Hill,  Providence,  Rhode  Island,  a  glaciated  ridge  of  the  Carboniferous 162 

VI.  Carboniferous  sandstones  at  Silver  Spring,  Rhode  Island 166 

VII.  Carboniferous  sandstones  near  Attleboro,  Massachusetts  176 

VIII.  Medium-sized  conglomerate,  Attleboro,  Massachusetts 176 

IX.  Ripple-marked  vertical  sandstones,  Attleboro,  Massachusetts 178 

X.  Raindrop  imprints  on  vertical  strata,  Attleboro,  Massachusetts 178 

XI.  Plainville  Valley,  Wrentham,  Massachusetts 180 

XII.  Vertical  bed  of  Dightou  conglomerate  at  Attleboro,  Massachusetts 181 

XIII.  Near  view  of  Dighton  conglomerate,  Attleboro,  Massachusetts 184 

XIV.  Selected  waterworn  and  indented  pebbles  from  Dighton  conglomerate,  Attleboro, 

Massachusetts _ 186 

XV.  Vertical  Carboniferous  sandstones,  Plainville,  Massachusetts 186 

XVI.  General  view  of  surface  at  AVest  Mansfield,  Massachusetts 188 

XVII.  Geological  map  of  the  northern  and  eastern  portions  of  the  Narragansett  Basin  . .  210 

Pis.    3.  Diagram  showing  misleading  synclinal  exposures  of  similar  strata 102 

4.  Exposure  of  disconnected  dike  in  Lime  Rock  quarries,  Rhode  Island 108 

5.  Sketch  map  of  distribution  of  upper  Cambrian  pebbles 110 

6.  Map  showing  distribution  of  metamorphosed  Carboniferous  rocks 120 

7.  Map  showing  general  outline  of  the  Narragansett  Basin _ _ 121 

8.  Section  across  eastern  arm  of  the  basin 122 

9.  Outline  map  and  general  cross  section  of  the  northern  jiart  of  the  basin 123 

10.  Edward  Hitchcock's  cross  section  of  the  Carboniferous  area 123 

11.  Map  showing  distribution  of  red  sediments 142 

12.  Geological  section  northward  from  Robinson  Hill 145 

13.  Diagram  showing  disappearance  of  Wamsutta  group  in  the  Coal  Measures.. 148 

14.  Section  through  felsite  knob  in  Attleboro,  Massachusetts 153 

15.  Geological  section  in  the  Millers  River  region 156 

16.  Geological  section  in  the  Arnolds  Mills  region 1.57 

17.  Hypothetical  geological  section  east  and  west  through  Providence,  Rhode  Island 160 

18.  Folded  and  faulted  Carboniferous  shales  at  Pawtucket,  Rhode  Island 162 

19.  Sketch  of  zone  of  excessively  jointed  sandstones,  face  of  McCormick's  quarry 166 

20.  Geological  section  from  VVatchemocket  Cove  to  Riverside,  Rhode  Island 166 

21.  Geological  section  through  rocky  islets  at  Halsey  Farm,  Silver  Spring,  Rhode  Island  ..  167 

22.  Geological  section  of  rocky  headland  near  Silver  Spring,  Rhode  Island 168 

23.  Theoretical  section  of  folded  structure  on  western  margin  of  the  Narragansett  Basin..  169 

24.  Contemporaneous    erosion   with    unconformity  in    the    Carboniferous    at  Attleboro, 

Massachusetts 176 

25.  Diagram  showing  cross  bedding 178 

26.  Geological  section  of  Plainville  Valley  and  thrust  plane 183 

27.  Section  of  the  Mansfield  Coal  Measures igo 

28.  Geological  section  in  "Westville,  Massachusetts 199 

29.  Diagram  illustrating  the  case  where  boring  affords  a  satisfactory  test  for  coal  beds 208 

30.  Diagram  illustrating  the  case  where  trenching  affords  a  satisfactory  test  for  coal 208 

MON  XXXIII 7 

97 


Postscript. — After  the  pages  for  this  monograph  were  cast,  the  writer 
found  in  shaly  strata  opposite  Plaiuville  Station,  at  the  base  of  the  fault 
block  described  on  page  183,  the  footprints  of  a  small  vertebrate,  probably 
an  amphil^ian,  associated  with  rain  prints  and  mud  cracks. — J.  B.  W. 


GEOLOGY  OF  THE  NARRAGANSETT  BASIN. 

PAET  II.-THE   NORTHERN   AND   EASTERN   PORTIONS   OF 

THE  BASIN. 


By    J.    B.    WOODWORTH. 


CHAPTER  I. 
THE  PROBLEM  OF  STRATIGRAPHIG  SUCCESSION. 

In  the  autumn  of  1894  the  writer  was  assigned  the  task  of  reporting 
upon  the  stratigraphic  succession  of  the  Carboniferous  deposits  in  the  Nar- 
ragansett  Basin.  Previous  to  this  time,  during  the  summer  months  of  1891 
and  1892,  he  had  made  an  examination  of  portions  of  the  basin  which 
seemed  likely  to  afford  a  key  to  the  structure  of  the  beds.  In  the  autumn 
of  1894  and  during  the  field  season  of  1895  the  examination  of  the  field 
was  continued.  The  following  pages  set  forth  the  results  of  these  studies. 
While  more  was  effected  than  the  writer  personally  expected,  there  are 
many  questions  yet  to  be  determined  regarding  the  equivalency  and  thin- 
ning out  of  strata  and  the  tracing  of  horizons.  It  is  believed  that  the 
work  so  far  accomplished  serves  to  afford,  first,  a  truer  measure  of  the 
thickness  of  the  beds  than  has  heretofore  been  gained;  second,  a  nearly 
complete  analysis  of  the  structure  of  the  part  of  the  basin  studied;  and, 
third,  a  differentiation  of  the  beds  into  a  few  horizons  which  have  a 
geographical  value,  if  not  also  in  most  cases  a  local  chronological  value. 

The  opportunity  which  the  geologist  has  of  determining  the  succession 
of  the  strata  in  any  region  usually  increases  with  the  amount  of  uplift  and 
denudation,  since,  were  the  beds  of  a  basin  to  remain  in  the  condition  in 
which  they  were  deposited,  the  surface  of  only  the  topmost  stratum  would 
be  open  to  examination.     However,  if  uplift  and  denudation  proceed  so  far 


100  GEOLOGY  OF  THE  XARRAGAXSETT  BASIN. 

as  to  produce  excessive  complication  of  structure  on  the  one  hand  and 
to  remove  great  thicknesses  of  strata  on  the  other,  the  evidence  which 
the  geologist  seeks  for  the  reconstruction  of  ancient  deposits  may  be  too 
scanty  to  permit  him  to  obtain  satisfactory  results.  The  stratified  rocks  of 
the  Narragansett  Basin  long  since  ceased  to  lie  in  their  original  attitixdes, 
and  so  mixch  of  them  has  been  carried  away  by  erosion  that  their  strati- 
graphic  succession  can  be  made  out  only  with  difficulty  and  only  for  limited 
portions  of  the  field.  But  these  general  causes,  which,  by  reason  of  their 
long-continued  action  or  their  intensity,  have  worked  to  the  detriment  of 
geological  investigation  in  most  mountain-built  districts,  have  in  this  field 
been  reenforced  by  local  peculiarities  arising  fi'om  the  geographical  position 
of  the  area  and  from  events  of  recent  geological  occurrence. 

The  difficulties  encountered  in  making  out  a  complete  and  satisfactory 
succession  of  the  strata  of  this  field  may  be  stated  as  follows: 

REPETITION   OF   LITHOLOGICAL   CHARACTERS. 

The  duplication  in  texture  and  color  of  sediments  widely  separated 
chronologically,  but  in  close  juxtaposition,  either  by  superposition  through 
unconformable  deposition  or  by  folding  and  faulting,  is  a  source  of  doubt 
where  fossils  are  not  present  in  both  terranes.  Thus,  in  North  Attleboro, 
Massachusetts,  and  northward,  in  the  midst  of  an  area  occupied  by  red 
Carboniferous  shales,  sandstones,  and  conglomerates,  there  appear  red 
Cambrian  shales  not  to  be  differentiated  in  most  localities  except  by  means 
of  the  contained  fossils.  Until  Cambrian  fossils  were  discovered,  the  red 
Cambrian  strata  were  included  by  all  observers  with  the  red  series  of  more 
recent  date. 

TRANSITION    OF    LITHOLOGICAL    CHARACTERS. 

By  gradation  in  the  size  of  the  particles  in  a  stratum,  a  conglomerate 
on  one  side  of  a  denuded  anticline  or  syncline  may  be  represented  by  a 
sandstone  or  shale  on  the  other  side  of  the  same  broad  fold.  In  like  man- 
ner, the  coloration  of  beds  may  vary  from  one  part  to  another  of  the  same 
basin,  so  that  strata  are  no  longer  distinguishable.  In  the  northwestern 
part  of  the  Nari-agansett  Basin  there  are  thick  beds  of  red  color,  having  a 
fairly  well  defined  stratigraphic  position.  Farther  south  these  beds  are 
replaced  by  others  of  dark-gray  color,  and  are  even  underlain  by  kinds 
of  beds  which  in  the  northern  area  always  overlie  the  red  series. 


LOCAL  CONDITIUNS  AFFECTING  OBSERVATION.  101 


EFFECTS  OP  IGNEOUS  INTRUSIONS. 


Igneous  intrusions,  by  inducing  litliological  changes,  often  render  the 
determination  of  the  equivalency  of  the  altered  strata  a  work  of  much 
labor,  particularly  where  the  alteration  is  but  one  of  several  obstacles  to 
the  tracing  of  the  stratigraphy.  Where,  owing  to  unfavorable  conditions 
at  the  present  surface,  the  contact  of  igneous  rocks  with  stratified  rocks  can 
not  be  observed,  much  perplexity  often  arises  as  to  the  order  of  events. 


METAMORPHISM. 


Dynamic  metamorphism  has  changed  both  the  texture  and  the  colora- 
tion of  the  rocks  of  extensive  sections,  thus  masking  the  original  sedimen- 
taiy  characters  and  rendering  the  recognition  of  horizons,  either  by  fossils 
or  by  litliological  peculiarities,  difficult.  Thus  the  Carboniferous  strata 
from  Wickford  north  to  Providence  are  highly  metamorphosed,  while  beds 
of  the  same  age  northeastward  in  the  basin  are  very  much  less  changed 
from  their  original  condition.  Ottrelite-schists  in  the  former  area  pass  into 
shales  in  the  latter  region. 


FOLDING    AND   FAULTING. 


While  folds  and  faults  directly  aid  investigation  by  bringing  to  the 
surface  strata  which  would  otherwise  be  concealed,  the  complete  inversion 
of  beds  and  the  separation  of  blocks  of  strata  by  faulting  result  in  con- 
fusion. In  the  series  of  red  strata  which  occur  in  North  Attleboro  the 
utmost  complication  has  arisen  through  the  degree  of  folding;  and  here, 
also,  a  block  of  strata  of  one  series  has  been  thrust  into  a  position  where 
it  is  surrounded  by  beds  of  a  different  horizon. 

DENUDATION. 

Where  beds  are  correlated  from  fold  to  fold  by  ph^'sical  indications, 
such  as  the  repetition  of  like  beds  in  the  same  order  and  with  the  same 
topography,  without  the  aid  of  fossils,  denudation  succeeded  by  local 
concealment  of  parts  of  the  series  by  deposition  may  lead  to  erroneous 
conclusions  in  the  matching  of  beds.  In  this  basin  there  is  a  group  of 
conglomerates  found  onl}^  in  synclinal  areas;  at  lower  horizons  are  other 
conglomerate  beds.  If  denudation  should  halt  upon  one  of  these  lower 
beds  where  it  is  exposed  in  the  axis  of   a  syncline,  doubt  would   arise, 


102 


GEOLOGY  OF  THE  NARRAGANSETT  BASIlSr. 


Fig.  3.— Diagram  showing  misleading  synclinal  exposures  of  similar  strata. 


without  otlier  means  of ,  correlation  than  these  physical  criteria,  as  to  which 
horizon  formed  the  axis  of  the  synclinal  structure.  Where  beds  have  been 
stripped  off  from  areas  several  miles  in  width,  as  between  the  Narragansett 

and  Norfolk  County  basins, 

._  \  ,,.- --,,  there  is  difficulty  in  making 

W     y'  y-'"      ""■-•-,   "\  /'      correlations.  Owingtodenu- 

''\  "  ,--''  ■-.,  \  /'  /      dation,  the  uppermost  beds 

,--''  ,.- ~,_  '"-.^        '-.,  '\  ,.-'  .,'''  of  a  formation,  as  originally 

deposited,  may  be  entirely 
lost.  Thus  there  is  doubt 
as  to  the  correlation  of  the 
upper  conglomerates  near 
Newport  with  those  in  the 
Taunton  syncline.  The  Newport  conglomerates  may  be  in  the  position  of 
the  left-hand  syncline  in  fig.  3,  while  those  near  Taunton  correspond  to  the 
upper  conglomerate  in  the  right-hand  svncline. 

GLACIATION. 

The  chief  difficulty  arising  from  g-laciation  is  the  coating  of  drift 
which  is  left  upon  the  rocks  of  a  country.  In  the  Carboniferous  tield  of 
southern  New  England  the  embarrassment  from  this  source  is  particularly 
great,  for  the  reason  that  the  area  received  a  thick  coating  of  the  deposits 
of  the  retreating  ice  sheet.  So  effectuall}-  are  the  bed  rocks  concealed  in 
parts  of  the  Carboniferous  basin,  that  outcrops  may  not  be  seen  oftener 
than  from  3  to  6  miles  in  any  direction.  The  tracing  of  highly  inclined 
strata  along  tlieir  strike  can  not  be  safely  undertaken  in  these  areas, 
and  the  mapping  of  the  formation  must  be  done  with  reference  to  the 
broadest  possible  groups,  or  perhaps  be  limited  to  the  indication  of  the 
presence  of  undiscriminated  members  of  a  large  rock  senes.  The  distri- 
bution of  frag'ments  of  rock  along  known  lines  of  glacial  carnage  is  some- 
times a  help  in  fixing  the  boundaries  of  the  underlying  bed  rocks.^  In  this 
field  the  transportation  of  bowlders  was  from  north  to  south.  Where  the 
rocks  trend  in  bands  from  east  to  west,  the  line  along  which  each  differ- 
ent kind  of  rock  appears  in  the  drift  is  approximately  the  boundary  line 


'  See  Fence- wall  geology,  by  A.  F.  Foerste :  Am.  Geol.,  Vol.  IV,  1889,  pp.  367-371. 


LOCAL  conditio:ns  affecting  observatiok  103 

between  it  and  the  band  of  rock  next  north.  Where  the  strata  strike  in  a 
northerly  direction,  the  fanning-  out  of  the  drift  southward  makes  the  deter- 
mination of  less  value;  but  trains  of  bowlders  thus  formed  are  frequently 
of  g-reat  use  in  checking  observations  upon  isolated  outcrops.  In  using 
this  method  less  reliance  is  to  be  placed  upon  waterworn  drift  than  upon 
ice-laid  deposits. 

SUBMERGENCE. 

Recent  depression  of  the  land  has,  in  the  immediate  vicinity  of 
Narragansett  Bay,  caused  the  flooding  of  old  valleys,  so  as  to  isolate  rock 
areas  in  the  form  of  islands  and  to  conceal  strata  which  might  otherwise  be 
open  to  examination.  To  a  certain  extent  this  difficulty  is  compensated  by 
the  good  exposures  in  the  cliffs  formed  along  the  seashore  by  the  action  of 
waves.  Such  natural  sections  occur  around  most  of  the  islands  in  the  bay 
and  along  the  coast  where  hard  rocks  come  to  the  surface,  as  far  north  as 
Providence. 

ABSENCE    OF    ARTIFKJIAL    EXCAVATIONS. 

The  almost  complete  absence  of  artificial  openings,  either  mines  or 
quarries,  in  this  field  at  the  present  day  has  limited  the  observations  here 
detailed  almost  entirely  to  surface  exposures.  The  quarries  which  exist 
are  mostly  in  the  granitic  rocks  bordering  the  basin,  and  it  is  only  from  the 
recorded  observations  of  previous  workers  that  information  regarding  coal 
mines  can  be  obtained. 

It  is  only  by  a  recognition  of  these  difficulties  and  their  combinations 
at  various  localities  in  this  field  that  the  geologist  realizes  the  checks  which 
it  is  necessary  to  apply  to  his  work  in  all  stages  of  its  advancement. 
These  difficulties,  along  with  a  formerly  jDrevailing  misapprehension  as  to 
the  nature  of  secondary  structure  in  rocks,  are  responsible  for  the  general 
belief  among  geologists  that  the  strata  of  this  area  are  too  much  broken  to 
be  unraveled.  On  taking  some  of  the  earlier-drawn  sections  of  the  strata 
of  this  basin  into  the  field,  it  will  be  seen  that  over  considerable  areas 
cleavage  was  mistaken  for  stratification,  metamorphosed  Carboniferous 
beds  were  taken  for  schists  of  much  earlier  date,  the  dips  of  strata  were 
averaged  where  they  should  have  been  analyzed  and  separately  repre- 
sented, and  more  reliance  was  placed  on  identity  of  color  than  this  feature 
is  worth  in  determining  the  identity  of  origin  of  sediments. 


CHAPTER     II. 
THE    PRE-CARBONIFEROUS   ROCKS. 

ALGOXKIAK  PERIOD. 

BLACKSTONE    SERIES. 

Primary  (limestone  and  hornbleurte  rocli).     C.  T.  Jaclcson:  Report  on  the  Geology  and  Agriculture  of 

Rhode  Island,  1840. 
Taeouic  (Stockbridge  limestone,  etc.).     E.Emmons:  Agriculture  of  Ne-n'  York,  Vol.  1, 18i6,  pp.  90-93 ; 

also  American  Geology,  Vol.  1, 1855,  p.  22. 
Moutalban.     W.  O.  Crosby :  Geology  of  Eastern  Massachusetts,  1880,  p.  128. 
Pre-Cambriau   (Hurouian?).     N.  S.  Shaler:    Bull.  Mus.  Comp.  Zool.  Harvard  Coll.,  Vol.  XVI,  1888, 

pp.  15-18. 

The  above-named  writings,  with  their  chronological  references,  as 
made  at  the  date  of  the  respective  papers,  set  forth  in  a  word  the  views 
advanced  regarding  the  age  of  the  series  of  limestones,  chloritic  and  horn- 
blendic  schists,  slates,  and  quartzites,  wliich  occur  in  the  lower  portion  of 
the  Blackstone  Valley  and  near  Providence,  within  the  limits  of  Rhode 
Island,  along  the  western  border  of  the  Carboniferous  basin.  It  evidently 
has  been  the  common  opinion  of  geologists  that  these  rocks  are  older  than 
the  Paleozoic  series  The  names  here  introduced,  without  a  geological 
map,  are  intended  as  locality  terms  only. 

The  Carboniferous  strata  of  this  basin  rest  everj^where  unconformably 
on  older  rocks,  which  are  found  immediately  bordering  the  basin  or  as 
small  inliers  within  its  limits.  These  inliers  are  Cambrian  sediments,  with 
associated  igneous  rocks.  The  pre-Cambrian  or  Algonkian  rocks  above 
referred  to  as  the  Blackstone  series  occur  in  the  form  of  highly  inclined 
masses  of  strata  separated  and  penetrated  by  granitic  intrusions  or  bath- 
olites.  The  area  of  these  clastic  and  the  associated  igneous  rocks,  now 
exposed  at  surface  along  the  western  border  from  Cumberland  southward 
in  Rhode  Island,  is  about  equally  divided  between  the  two  groups.  The 
thorough  disruption  of  these  ancient  strata  by  changes  of  attitude  and 
igneous  intrusion  has  produced  in  the  area  a  type  of  structure  which  may 

104 


THE  BLACKSTONE  SERIES.  105 

well  be  termed  a  batliolitic  complex.  Notwithstanding  the  irregular  dis- 
position of  the  detached  masses  of  strata,  there  is  traceable  a  dominant 
structural  system  in  this  belt  which  is  nearly  east  and  west  in  its  trends. 
The  strikes  of  the  strata  in  the  Blackstone  Valley  are  NW.-SE.;  those 
in  the  area  west  of  Providence,  nearly  E.— W.  Members  apparently  of  an 
equally  ancient  system  of  rocks  occur  on  the  southeast  of  the  basin  in  the 
gneisses  and  schists  of  the  New  Bedford  area  (see  fig.  7,  p.  121),  and  in 
small  masses  near  Canton  Junction. 

The  geological  relations  of  the  Blackstone  series  are  not  exactly 
defined  along  the  northern  and  western  border.  The  lowest  stratified 
member  along  this  border  of  the  basin  has  not  been  seen,  in  the  area  under 
discussion,  to  rest  on  the  necessarily  older  land  mass  from  which  it  was 
derived.  This  separation  is  probably  due  to  the  intrusion  of  granitic 
masses. 

The  determination  of  the  pre-Cambrian  age  of  the  group  of  limestones, 
schists,  slates,  and  quartzites,  in  the  Blackstone  River  area,  rests  upon  the 
relation  which  it  bears  to  the  lower  Cambrian  sti-ata  in  North  Attleboro. 
The  Olenellus  fauna  occurs  in  little-altered,  red,  calcareous  shales  and  slates 
at  this  latter  place  in  close  proximity  to  granite  (hornblendic  granitite). 
Four  miles  west  of  this  inlier  of  the  Carboniferous  area  occur  the  sedi- 
ments involved  in  the  complex  already  described.  These  strata  are  higlily 
altered  sediments,  now  hornblendic  and  chloritic  schists,  mainly  of  a  green 
color,  altered  sandstones  or  quartzites,  and  crystalline  limestones.  The 
presumption  that  these  rocks  are  pre-Cambrian  rests,  at  present,  therefore, 
on  the  difference  in  metamorphism  between  them  and  the  lower  Cambrian 
rocks  in  the  same  field.  The  criterion  apjsealed  to  in  this  case  is  embodied 
in  the  statement  that  where  two  sets  of  rocks  coexist  in  the  same  dynamic 
field,  that  group  which  has  undergone  one  dynamic  movement  more  than 
the  other  is  the  older.  If  this  view  is  maintained,  this  series  of  rocks  falls 
into  the  Algonkian.  Evidence  of  unconformity  with  the  lower  Cambrian 
is  necessary  to  make  this  conclusion  positive.  The  relation  of  the  granitic 
intrusives  to  the  pre-Cambrian  on  the  one  hand  and  to  the  Cambrian  on  the 
other  is  simply  to  show  that  the  granitite  is  younger  than  the  former,  and 
that  the  sedimentary  rocks  are  of  different  ages. 

From  the  typical  development  of  this  series  in  tlie  lower  course  of  the 
Blackstone  River  between  Woonsocket  and  Pawtucket,  it  is  here  proposed 


106  GEOLOGY  OF  THE  NAREAGANSETT  BASIN. 

to  refer  to  the  rocks,  exclusive  of  the  igneous  intrusives,  as  the  Blackstone 
series.  On  hthological  grounds,  which  have  some  support  in  the  stra- 
tigraphy, the  series  may  be  divided  into  the  Cumberland  quartzites,  the 
Ashton  schists,  and  the  Smithfield  limestones. 

CUMBERLAND    QUARTZITES. 

Bands  of  quartzite  occur  as  discontinuous  outcrops  at  several  localities. 
The  principal  of  these  is  traceable  from  the  southern  side  of  Sneech  Pond, 
along  the  main  street  southeastward  for  a  mile  and  a  half  in  the  village  of 
Cumberland  Hill.  The  width  of  outcrop  varies  from  500  to  1,500  feet. 
Another  small  exposure  occurs  on  the  same  general  trend  2  miles  north  of 
Ashton.  A  broad  belt  of  outcrops  of  the  rock  occurs  in  the  valley  of  the 
Blackstone  from  Cumberland  village  southeastward.  The  quartzite  is 
interbedded  with  schists  or  green  slates  in  alternations  of  varying  thickness. 
The  dip  of  the  structure  is  NE.  at  angles  from  50°  upward. 

At  Albion  Mr.  F.  C.  Schrader  has  observed  fragments  of  the  quartzite 
in  a  siliceous  and  quartzitic  schist  striking  about  N.  41°  W.  and  dipping 
50°  NE.  Just  Avest  of  this  outcrop,  and  separated  from  it  by  a  small  ravine, 
is  a  large  outcrop  of  the  quartzite.  The  presumption  here  is  that  of  an 
unconformable  relation  of  the  Ashton  schists  upon  the  quartzite.  The 
quartzite  is  lithologically  the  same  as  the  Cumberland  rock.  The  fragments 
of  the  quartzite  in  the  Ashton  schists  are  sometimes  somewhat  worn.  The 
schist  in  the  bold  bluff  on  the  east  of  Sneecli  Pond  also  contains  small, 
rounded,  and  broken  fragments  of  the  quartzite.  These  facts,  together 
with  the  siliceous  character  of  the  slates  and  schists,  indicate  that  they  were 
derived  from  the  erosion  of  a  quartzite  terrane.  Some  evidence  of  probable 
unconformity  of  dip  at  the  Albion  locality  also  points  to  the  conclusion 
that  the  more  massive  quartzite  beds  of  the  Blackstone  series  are  older 
than  the  Ashton  schists. 

Limited  exposures  of  quartzite  occur  along  the  border  in  the  western 
part  of  Providence  at  Manton.  The  quartzites  are  prevailingly  brownish- 
yellow  in  color  wherever  they  occur,  are  generally  granulated  by  crushing, 
and  are  glossy  by  reason  of  the  development  of  some  sericite.  Their 
occurrence  in  lenses  and  along  strike  lines,  together  with  the  probability 
that  they  are  older  than  the  Ashton  schists,  seems  to  indicate  that  the 


THE  BLACKSTOI^E  SERIES.  107 

exposures  at  the  present  surface  are  due  to  the  truncation  of  close-pressed 
folds  in  which  the  quartzites  occupy  anticlinal  axes. 

ASHTON    SCHISTS. 

Reasons  have  been  advanced  above  which  make  it  probable  that  the 
argillaceous  rocks  of  the  Blackstone  series  are  the  finer  sediments  succeed- 
ing the  deposition  and  partial  erosion  of  the  Cumberland  quartzites.  Dis- 
tinctions in  the  several  broad  bands  of  these  rocks  may  be  based  upon  the 
prevalence  of  siliceous  sediment  on  the  one  hand  and  of  the  chloritic  and 
hornblendic  metamorphic  products  on  the  other.  Not  less  manifest  are 
differences  of  secoiidary  structure,  on  which  the  slaty  and  schistose  char- 
acter of  the  beds  in  many  places  depends.  All  along  the  border  of  the 
area,  where  the  rocks  are  in  contact  with  granitite  and  quartz-porphyry, 
zones  of  local  metamorphism  occur  in  which  the  characteristic  effects  of 
igneous  intrusions  are  to  be  observed.  The  series  as  a  whole  is  character- 
ized by  its  greenish  color.  Some  of  the  rocks  included  in  the  schists  are 
jDrobably  of  igneous  origin. 

SMITHFIELD    LIMESTONES. 

Owing  to  the  setting  off  of  Lincoln  from  Smithfield  in  1871,  the  areas 
of  limestone  formerly  designated  by  the  name  here  used  are  no  longer  in 
the  town  of  that  name.  The  areas  of  this  rock  are  isolated,  ovoidal  in  out- 
line, and  have  no  very  systematic  distribution.  In  the  main,  they  lie  near 
granitic  masses,  as  between  the  valleys  of  the  Blackstone  and  Moshassuck 
rivers.  The  areas  are  a  mile  or  more  apart.  Those  in  the  area  referred  to, 
including  Lime  Rock,  are  in  general  along  the  same  horizon  in  the  Black- 
stone series.  Most  of  the  areas  are  in  the  Blackstone  Valley,  but  there  are 
other  outcrops  south  of  the  Smithfield  granitic  mass,  in  North  Providence 
and  Cranston. 

The  limestone  are  finely  granular,  dolomitic,  crystalline  aggregates, 
and  have  a  laminated  structure.  Shear  zones  with  development  of  chloritic 
minerals  are  common.  The  rocks  have  been  subjected  to  extensive  shear- 
ing and  crushing  movements,  with  the  consequent  faulting  of  small  dikes, 
as  in  the  Lime  Rock  quarries.  The  limestone  occupying  the  space  between 
these  dismembered  dikes  shows  to  the  eye  no  trace  of  the  separation.     Tlie 


108 


GEOLOGY  OF  THE  NAREAGANSETT  BASIN. 


disjoined  parts  of  a  small  dike  of  ampliibolite/  probably  altered  diabase, 
had,  ill  1887,  the  appearance  shown  in  the  accompanying  diagram  (fig.  4). 
The  contact  relations  of  the  limestones  with  the  schists  which  inclose 
them  have  not  been  satisfactorily  determined,  by  reason  of  the  lack  of  good 
exposures.  So  far  as  the  evidence  yet  obtained  goes,  the  limestones  appear 
to  be  of  sedimentary  origin,  though  no  trace  of  fossils  has  been  found  in 
them.  The  lack  of  continuity  in  the  exposures  is  probably  due  to  com- 
pressive movements  in  the  formation  of  a  closely  folded  series.  It  is 
probable  that  the  ovoidal  form  of  the  outcrops  as  represented  on  maps 
would  have  to  be  made  eUiptical,  or  even  pointed  at  the  ends,  if  better 
exposures  existed. 

On  the  hypothesis  of  close  folding,  which  alone  can  account  for  the 

great  breadth  of  outcrop  of  this 
series  on  the  western  side  of  the 
Carboniferous  basin,  the  thicker 
limestones,  if  newer  than  the  slates, 
would  fall  in  synclinal  axes. 

In  the  bed  of  a  small  brook 
above  the  old  iron  mine  in  Crans- 
ton a  vertical  bed  of  limestone  may 
be  seen  between  the  beds  of  slate. 
The  limestone  has  a  thickness  of 
about  10  feet.  It  here  seems  to  be  an  intercalated  bed.  As  yet  no  facts 
have  been  discovered  to  show  whether  the  limestones  are  of  the  same  age  as 
or  newer  than  the  slates  and  schists.  It  is  clear  that  some  of  the  limestones 
are  not  older  than  the  argillaceous  series. 

The  most  conspicuous  feature  of  the  limestone  areas  is  the  occasional 
association  with  them  of    metalliferous   deposits.     The  richest   and   most 


-Exposure  of  discoimected  dike 
Rhode  Island. 


Lime  xlock  quarries, 


1  Amphibolite  from  Lincoln.  This  rock  occurs  in  the  southernmost  limestone  locality  at  Lincoln, 
Ehode  Island.  Microscopic  characters :  Hornhlende  occurs  in  the  slide,  with  extinction  parallel  to 
shorter  diagonal  of  rhombs.  Chlorite  is  present  in  large  quantities.  Muscovite  occurs  in  confusedly 
arranged  irregular  lamina?.  Titauite  occurs  in  cleavage  forms,  derived  probably  through  leucoxene 
from  decomposition  of  titaniferous  magnetite.  Magnetite  in  some  areas  still  exhibits  a  kernel  of  the 
unaltered  miueral.  Apatite  occurs  partly  or  wholly  iuclosed  by  the  titanite.  The  highly  altered 
condition  of  this  rock  renders  its  determination  doubtful.  Quartz  occurs  in  small  areas,  where  it  is 
probably  of  secondary  origin.  Notwithstaudiag  the  abseuce  of  the  feldspar  constituent,  the  nature 
of  the  hornblende  makes  it  probable  that  the  rock,  now  an  amphibolite,  was  originally  a  diabase,  like 
many  other  highly  altered  dikes  in  southern  New  England. 

Mr.  Schrader  reports  other  dikes  near  the  western  margin  of  the  Blackstone  series  in  the  valley 
of  the  Moshassuck  River.     There  are  also  in  this  field  apophyses  from  the  granitic  rocks. 


UPPER  CAMBRIAN  PEBBLES.  109 

varied  of  these  is  in  the  northern  part  of  the  town  of  Cumberland,  where, 
in  the  area  about  Sneech  Pond,  ores  of  copper  and  iron  occur,  rephxcing 
portions  of  the  Hmestone,  angular  brecciated  fragments  of  which  lie  in 
the  ore-bearing  mass.  The  iron  of  the  old  mine  in  Cranston,  in  the  "dug- 
way,"  is  probably  a  ferruginous  replacement  of  the  limestone.  The  Sneech 
Pond  ore  bodies  above  mentioned  are  near  eruptive  rocks,  but  whether  the 
deposits  have  originated  through  the  action  of  heated  waters  or  through  the 
downward  percolation  of  acidulated  surface  waters,  the  field  itself  does  not, 
in  the  present  condition  of  the  openings,  give  opportunity  for  determining. 

CAMBRIAK  PERIOD. 

LOWER    CAMBRIAN. 

Rocks  comprised  within  the  limits  of  the  formations  now  denominated 
Cambrian  were  referred  to  vaguely  as  early  as  1844  by  Ebenezer  Emmons, 
but  the  discovery  of  demonstrable  Cambrian  strata  in  this  field  was  not 
announced  until  1888,  when  Professor  Shaler  and  Dr.  A.  F.  Foerste  pub- 
lished the  account  of  the  fossils  found  by  them  in  North  Attleboro,  Massa- 
chusetts. For  a  further  notice  of  these  rocks  the  reader  is  refen-ed  to  Dr. 
Foerste's  description  in  Part  III  of  this  monograph. 

MIDDLE    CAMBRIAN. 

Beds  of  Middle  Cambrian  age  have  not  been  discovered  south  of  the 
area  about  Weymouth  and  Braintree,  where  they  are  known  to  occur. 

UPPER  CAMBRIAN. 

{Not  known  in  place.) 

Postdam.     W.  B.  Kogers:  Proc.  Boston  Soc.  Nat.  Hist.,  Vol.  VII,  1861,  pp.  389-391. 
Primordial.     Crosby  and  Barton:  Am.  Jour..Soi.,  3d  series,  Vol.  XX,  1880,  pp.  416-420. 
Upper  Cambrian.     C.  D.  Walcott:  Am.  .Jour.  Sci.,  4tli  series,  Vol.  VI,  1898,  pp.  327-328. 

In  1861  it  was  pointed  out  that  the  coarse  conglomerates  of  the  southern 
poi-tion  of  the  Carboniferous  field  contained  quartzite  pebbles  carrying  two 
species  of  Lingula  (L.  prima  and  L.  antiqua)  referable  to  the  Potsdam  sand- 
stone. In  1880  Crosby  and  Barton  announced  the  occurrence  of  Scolithus 
linearis  in  the  same  conglomerate  pebbles  near  Newport,  Rhode  Island. 

During  the  present  survey  the  writer  has  Yound  these  fossiliferous 
pebbles  farther  north  and  east  than  the  localities  described  by  earlier 
investigators.     Other  occurrences  are  noted  in  Dr.  Foerste's  section  of  this 


110 


GEOLOGY  OF  THE  jS^ARRAGANSETT  BASIN. 


monogTiiph.  Lingulse  (now  Obolus,  see  p.  113)  were  found  in  a  pebble  in  the 
red  Carboniferous  conglomerate  on  the  east  bank  of  Abbots  Run,  between 
Lanesville  and  Arnolds  Mills,  Rhode  Island.  Eastward  an  Obolus  pebble 
was  found  on  the  beach  near  Marshfield,  Massachusetts,  together  with  a 
large  fragment  of  quartzite  carrying  the  long,  parallel,  closely  set  burrows 
of  Scolithus  linearis.     Botli  of  these  frao-ments  weva  within  the  Dossible  ransre 


Fig.  5. — sketch  map  of  distribution  of  upper  Cambrian  pebbles.     The  uorth-south  lines  represent  the  supposed  direction 
of  glacial  motion  during  the  maximum  development  of  the  jS'ew  England  glacier. 

of  glacial  streaiu  drift  from  the  northeasternmost  outcrops  of  Carboniferous 
conglomerate  in  the  main  basin. 

In  July,  1895,  I  found  a  small  sand-blasted  Obolus  pebble  on  the  cliff 
near  Highland  Light  in  Truro,  at  the  northern  extremity  of  Cape  Cod;  and 
another  pebble,  carrying  the  same  brachio^Dod,  was  found  in  an  ancient 
beach  on  the  ocean  side  of  Provincetown.  These  pebbles  are  so  far  to  the 
east  of  the  known  Carboniferous  conglomerates  on  the  mainland  that  their 
dei'ivation  from  the  main  basin  or  from  the  Norfolk  Basin  seems  improbable, 
particularly  for  the  reason  that  the  movements  of  the  glacial  currents  and 


UPPER  CAMBRIAN  PEBBLES.  Ill 

the  drainage  from  the  ice  which  were  concerned  in  the  distribution  of  the 
pebbles  seem  to  demand,  in  our  present  knowledge,  an  origin  from  some 
point  in  Massachusetts  Bay,  as  will  be  seen  from  an  examination  of  the 
accompanying  outline  map  (fig.  5)  of  the  lines  of  glacial  flow  in  eastern 
Massachusetts  during  the  time  of  formation  of  the  Cape  Cod  moraine.  It 
is  true  that  in  the  closing  stages  of  ice  retreat  there  are  indications  about 
Boston  of  a  more  easterly  set  in  the  ice,  as  if  it  were  controlled  by  the  local 
slope  to  the  sea.  If  this  movement  extended  as  far  south  as  the  Duxbury 
shore,  the  derivation  of  the  pebbles  from  the  northernmost  areas  of  con- 
glomerate may  be  accounted  for;  but  these  fossiliferous  pebbles  have  not 
been  found  as  yet  in  the  Norfolk  and  Boston  areas,  either  in  the  con- 
glomerates or  in  the  glacial  drift,  though  quartzite  pebbles  abound.  Glacial 
striae  on  a  granitic  ledge  in  Marshfield  gave  a  reading  of  several  degrees 
west  of  north,  but  this  locality  is  in  the  region  of  the  Pljaiiouth  inter- 
lobate  moraine,  and  does  not  indicate  that  the  ice  moved  beyond  this  line 
of  accumulation  in  this  direction  to  the  eastern  shore  of  Cape  Cod  Baj^. 

The  Obolus  pebbles  are  very  abimdant  in  the  beaches  of  the  south 
coast,  as  far  east  as  Nantucket  and  as  far  west  as  Block  Island,  being 
most  common  in  the  intermediate  area  on  Marthas  Vineyard.  The  pebbles 
have  been  dispersed  southward  by  the  glaciation  of  the  Carboniferous 
ledges  of  the  mainland. 

The  earlier  reference  of  these  fossiliferous  quartzites  to  the  epoch  of 
the  Potsdam  sandstone  has  recently  been  confirmed  by  Walcott,^  who  states 
that  the  brachiopods  have  their  closest  affinity  in  the  upper  Cambrian 
fauna  of  the  Newfoundland  area.  As  yet  the  beds  have  not  been  found 
in  situ,  an  >  little  else  is  positively  known  regarding  the  upper  Cambrian 
formation  of  this  portion  of  New  England  than  that  which  may  be  inferred 
from  a  collection  of  these  pebbles.  The  information  thus  obtained  may  be 
briefly  stated  as  follows. 

Neglecting  the  question  of  superposition  and  the  alternation  of  similar 
beds  with  like  faunas,  data  for  which  matters  are  of  course  wanting  in  the 
pebbles,  the  upper  Cambrian  of  the  area  whence  the  pebbles  came  appears 
to  have  been  composed  of  at  least  these  three  biological  divisions: 

1.  An  Obolus  sone  of  light- colored  quartzites. — The  pebbles  of  this  zone  exhibit 
bands,  3  or  4  inches  thick,  of  these  gregarious  shells,  usually  preserved  as  black  gra- 

'  Letter  to  Professor  Shaler. 


112  GEOLOGY  OF  THE  NARRAGANSETT  BASIN. 

phitic  crusts,  and  less  commouly  as  white  calcareous  shells.  The  shell ;  occur  mostly 
as  detached  valves,  with  their  concave  or  interior  faces  turned  downward  upon  the 
bedding  planes,  evidently  as  the  result  of  current  action  strong  enough  to  invert  the 
shells  when  their  saucer-shaped  edges  were  opposed  to  the  bottom  drift,  but  not 
powerful  enough  to  move  them  when  their  smooth  oval  backs  were  presented  to  the 
moving  water.  The  existence  of  currents  and  shallow-water  conditions  is  further 
attested  by  examples  of  pebbles  with  marked  ci'oss  bedding,  the  "top-set"  layers  of 
which,  with  contained  shells,  confirm  the  explanation  here  given  for  the  position  of 
detached  brachiopod  valves. 

The  variations  in  the  quartzitea  and  the  irregularities  in  the  fossiliferous  layers 
suggest  that  this  zone  alternated  with  bands  of  barren  quartzite,  described  as  ISTo.  3. 

2.  A  Scolithus  linearis  zone  of  lif/ht-colored  quartzites. — Pebbles  carrying  Scolithus 
are  by  no  means  so  common  as  the  Obolus  pebbles;  they  are  most  abundant  in  the 
beaches  of  Marthas  Vineyard.  A  cobble  found  on  the  beach  of  Marshfield  Keck  was 
lOi-  inches  long,  6  inches  thick,  and  6  inches  across,  the  burrows  being  C  inches  long 
and  worn  off  at  both  ends.  Walcott  notes  their  absence  from  the  materials  which  he 
studied. 

3.  A  barren  zone  or  zones  of  quartzites  of  various  colors. — Some  of  the  quartzite 
pebbles  included  under  this  head  may  be  of  other  than  upper  Cambrian  age.  since 
quartzites  of  different  periods  occur  along  the  western  margin  of  the  basin. 

A  few  quartzite  pebbles  traversed  with  quartz  veins  older  than  the 
Carboniferous  sediments  have  been  observed,  from  which  it  is  to  be  inferred 
that  the  iipper  Cambrian  formation  underwent  some  deformation  attended 
by  the  segregation  of  silica  in  veins  while  the  beds  were  still  deeply 
buried,  but  under  what  depth  of  cover  is  not  exactly  known.  The  presence 
of  Silurian  fossils  in  the  Miocene  gravels  of  Marthas  Vineyard  maj^  indicate 
the  continuance  of  deposition  in  tlais  field  during  the  succeeding  Silurian 
period. 

Until  fossils  are  found  in  the  quartzites  which  are  known  to  occur  in 
the  outlying  region,  the  exact  source  of  the  pebbles  in  the  Carboniferous 
conglomerates  must  remain  in  doubt.  It  should  be  noted  that  the  erosion 
of  pre-Carboniferous  quartzites  has  fm-nished  at  least  three-fourths  of  the 
coarse  fragmental  material  in  the  Carboniferous  grits  and  conglomerates. 
The  area  of  erosion  of  so  much  coarse  material,  ranging  to  pebbles  a  foot 
or  more  in  diameter,  as  must  have  been  the  case  with  the  now  elongated 
quartzite  pebbles  of  the  conglomerate  at  Newport,  could  not  have  been  far 
distant. 

While  the  preponderance  of  large  quartzite  pebbles  and  fossiliferous 
examples  in  the  southern   portion  of   the   Carboniferous   field   favors  the 


UPPER  CAMBRIAN  PEBBLES.  113 

idea  that  the  derivation  was  from  the  south  and  east,  the  evidence  is 
good  only  for  the  pebbles  in  that  part  of  the  area.  The  quartz  pebbles  on 
the  north  and  west  may  equally  well  have  been  derived  from  those 
directions  for  all  that  is  known  regarding  the  neighboring  areas,  particu- 
larly since  the  texture  of  the  Carboniferous  deposits  is  mainly  consonant 
with  the  hypothesis  of  a  peripheral  origin  of  the  sediments  contained 
within  the  present  limits  of  the  basin. 

In  conclusion,  it  need  only  be  said  that  there  appears  to  have  been 
nearly  continuous  deposition  in  this  field  throughout  the  Cambrian  period, 
for  though  the  middle  Cambrian  has  not  been  identified  south  of  Braintree, 
it  lies  within  the  same  geological  province.  The  change  from  the  mud  of 
middle  Cambrian  times  to  sandy  bottoms  of  upper  Cambrian  times  in  this 
portion  of  New  England  apparently  indicates  progressive  shoaling  and 
uplift  of  the  sea  floor. 

Since  the  above  account  was  written,  Walcott^  has  published  a  careful 
revision  of  the  fauna  of  these  fossiliferous  pebbles,  referring  the  forms  to 
Obolus  (Lingulobulus)  affinis  Billings  and  0.  (i.)  spissus  Billings,  and  to  a 
new  species  Ohohis  (Lingulella)  rogersi.  Walcott  suggests  the  derivation  of 
the  fragments  from  an  area  of  erosion  lying  in  the  vicinity  of  Newfoundland. 

SILUKIAN  PERIOD. 

There  are  no  known  clastic  rocks  of  Silurian  age  in  situ  in  this  basin. 
Certain  terranes  in  the  southern  and  western  parts  of  the  area  formerly 
referred  to  this  period  are  now  regarded  as  either  Cambrian  or  Carboniferous. 

CHBBT   PEBBLES. 

The  possible  former  existence  of  a  Silurian  formation  in  this  portion 
of  the  coast  is  indicated  by  the  occurrence  of  chert  pebbles  carrying 
upper  Silurian  corals  in  the  Miocene  gravels^ — the  "osseous  conglomerate" 
of  Hitchcock — at  Gay  Head  and  elsewhere  on  Marthas  Vineyard.  I  am 
indebted  to  Mr.  C.  D.  Walcott  for  the  determination  of  the  age  of  these 
chert  pebbles.^  Their  origin  is  involved  in  the  same  mystery  which  sur- 
rounds the  upper  Cambrian  pebbles. 

'  Note  on  tlie  braoMopod  fauna  of  the  quartzitic  pebbles  of  the  Carboniferous  conglomerates  of 
the  Narraganaett  Basin,  Rhode  Island,  by  C.  D.  Walcott:  Am.  Jour.  Sci.,  4th  series,  Vol.  VI,  1898,  pp. 
327-328. 

-  In  an  early  notice  of  them,  based  on  scanty  material,  I  mistook  the  single  coral  then  found  for 
a  Cambrian  form.     Am.  Geologist,  Vol.  IX,  1892,  pp.  243-247. 
MON  XXXIII 8 


CHAPTER     III. 

THE  IGNEOUS  ROCKS  OF  THE   BORDER  OF  THE  BASIN. 

GRANITIC    ROCKS. 

The  granitic  rocks  which  border  this  basin  from  Wrentham  eastward 
and  thence  along  the  margin  in  Plymouth  County  southward  and  westward 
to  Fall  River  are  designated  Archean  on  the  most  recent  maps.  The  rocks 
are  mainly  hornblendic  granitites.^  The  opinions  which  have  been  published 
regarding  the  origin  and  time  of  eruption  of  these  rocks  are  various  and 
often  contradictory.  Edward  Hitchcock,  if  he  can  be  said  to  have  held  a 
definite  opinion  upon  the  subject,  was  inclined  to  represent  the  granitic 
masses  as  erupted  after  the  Carboniferous  formations  were  deposited.  In 
1882  Wadsworth  clearly  showed  that  the  hornblendic  granitites  in  Braintree 
are  erupted  through  slates  now  known  to  be  of  middle  Cambrian  age.  The 
granitite  of  that  locality  is  then  more  recent  than  the  middle  Cambrian. 
Except  for  a  few  detached  areas,  all  around  the  border  of  this  part  of  the 
basin  the  granitite  extends  beneath  the  Carbonifei'ous  basal  beds,  which  are 
in  large  part  made  up  of  the  little-worn  waste  from  the  granitite.  At  no 
point  in  the  northern  half  of  the  field  has  true  granite  been  found  in 
eruptive  contact  with  Carboniferous  sediments. 

The  coarsely  crystalline  texture  of  the  granitite  along  most  of  the 
margin  indicates,  according  to  the  accepted  opinion,  that  the  rock  which  is 
now  exposed  at  surface  crystallized  at  a  depth  and  under  a  cover  of  some 
thickness,  ^^robably  in  part  of  sedimentary  rocks  removed  from  this  portion 
of  the  area  before  Carboniferous  deposition  set  in.  Some  of  the  Cambrian 
formations  undoubtedly  formed  part  of  this  cover.  No  small  depth  of  the 
granitite  must  likewise  have  been  canned  away.  At  Braintree  the  zone  of 
granitite  with  a  finer  texture,  due  to  the  more  rapid  cooling  near  contact 
with  the  slates,  is  preserved,  and  gives  a  minimum  thickness  of  several 
scores  of  feet  between  the  contact  and  the  inner  coarsely  crystalline  rock. 

Although  the  several  varieties  of  granitic  rocks  in  the  area  named  are 

'  The  "  syenite  "  of  Edward  Hitchcock  and  earlier  writers. 


GRANITIC  EOCKS.  115 

essentially  coterminous,  these  variations  ai-e  of  sufficient  extent  to  be  indicated 
when  the  mapping  of  their  areas  is  undertaken.  All  about  the  northern  mar- 
gin, j^articularly  near  the  Norfolk  County  Basin,  where  the  red  Carbonifer- 
ous sediments  abound,  the  feldspar  of  the  granitite  is  in  many  localities  of  a 
deep-red  color.  The  association  of  these  red  feldspars  with  the  red  Carbonif- 
erous rocks  along  this  northern  border  of  the  field  maybe  without  significance, 
but  the  relation  is  noteworthy.  The  coloration  of  the  feldspar,  however, 
has  arisen  apparently  through  the  penetration  of  an  iron  oxide  in  solution, 
following  upon  atmospheric  decay.  The  oxidation  of  the  iron-bearing  sili- 
cates in  the  granitite,  e.  g.,  the  biotite  and  the  hornblende,  may  have  fur- 
nished the  iron,  in  which  case  there  is  no  reason  for  supposing  that  the 
coloring  matter  has  leached  downward  from  the  formerly  overlying  red 
Carboniferous  beds.  On  the  contrary,  it  is  more  probable  tliat  the  red  beds 
owe  their  color  to  this  iron  oxide  ha\ang-  been  set  free  in  pre-Carboniferous 
times.  The  surface  exposures  of  this  red  granitite  are  simply  the  underlying 
base  of  the  zone  of  decayed  rock  which  was  swept  off  in  the  making  of 
the  Carboniferous  sediments.  The  objection  which  may  be  raised  to  this 
view  is  that  the  granitite  has  been  at  least  twice  exposed  to  atmospheric 
decay,  once  in  pre-Carboniferous  times,  and  again  in  recent  geological 
times,  and  that  the  red  color  of  the  feldspars  to-day  may  be  due  to  recent 
rather  than  to  ancient  decay.  But  the  arkose  at  the  base  of  the  Carbonif- 
erous is  sufficient  proof  of  the  ancient  period  of  atmospheric  decay,  and 
the  immediately  overlying  red  beds  show  that  the  process  of  rock  discolor- 
ation by  percolating  iron  oxides  went  on  in  early  Carboniferous  time 
essentially  in  the  manner  advocated  by  Russell. 

The  possibility  of  the  coloration  of  sediments,  at  least  locally,  by  this 
means  is  attested  by  observations  Avhich  were  made  during  the  present 
survey.  At  one  point  in  the  region  of  red  granitite  I  was  struck  Avith 
the  redness  of  the  water  standing  in  the  bottom  of  a  small  test  quarr}^, 
and  with  the  film  of  red  mud  deposited  CA^erywhere  beneath  the  Avater 
level.  There  can  be  no  doubt,  therefore,  that  the  red  g-ranitites  are  at 
the  present  time  capable  of  staining  sediments  Avith  a  red  iron  oxide  film. 
This  process  seems  to  be  a  local  instance  contrary  to  the  general  A^ellowish 
and  brownish  hues  so  Avidely  noted  as  the  result  of  decomposition  of  rocks 
in  this  latitude.^ 

'  W.  O.  Crosby,  Am.  Geologist,  Vol.  VIII,  1891,  pp.  72-82. 


116  GEOLOGY  OF  THE  NAERAGANSETT  BASIN. 

Near  Easton  the  glacial  drift  from  the  granitite  area  carries  a  variety 
of  the  rock  of  bluish-white  color  with  large  crystals  of  hornblende  and 
prismatic  crystals  of  fegirine.  At  a  few  points  the  rock  becomes  fine 
grained  and  is  in  contact  with  undetermined  rocks,  presumably  pre- 
Carboniferous  elastics.  Such  contacts  may  be  observed  north  of  Mansfield 
and  near  Hanover  Four  Corners.  In  Montello,  north  of  Brockton,  the  gran- 
itite with  a  pink  feldspar  was  seen  to  contain  small  veins  of  prehnite. 

Along  the  eastern  border  of  the  basin,  in  Plympton,  there  also  is  a  fine- 
grained granitite.  Southward,  in  the  northern  part  of  the  area  represented 
on  the  Fall  River  sheet,  red  granitite  is  again  seen  in  bowlders,  and  the 
ordinary  phase  of  the  hornblendic  granitite  is  well  exposed  in  the  quarries 
at  Fall  River,  though  here  the  rock  has  been  locally  sheared  and  in  zones 
is  quite  gneissoid. 

In  conclusion,  it  can  not  be  said  that  the  facts  at  hand  warrant  a  more 
definite  statement  than  that  these  granitites  were  erupted  at  some  period 
betAveen  the  Carboniferous  and  the  middle  Cambrian.  The  granitic  rocks 
near  Providence  appear,  as  shown  on  page  105,  to  be  older. 

PLYMPTON   FELSITES. 

In  Plympton  and  extending  toward  Halifax  is  a  small  area  of  reddish 
and  greenish  felsites,  the  exact  limits  of  which  are  not  known.  At  one 
point  on  the  eastern  border  of  the  Carboniferous  area  the  felsite  in  the  form 
of  a  dike  several  feet  wide  may  be  seen  cutting  the  granitite.  North  of 
this  locality  is  the  main  occurrence,  in  the  form  of  a  flow,  the  bands  of 
which  dip  gently  westward  toward  the  Carboniferous  basin.  As  no  Carbon- 
iferous strata  are  seen  in  connection  with  the  igneous  rocks  at  this  point, 
their  age  is  not  definitely  known.  The  imperfect  exposures  seem  at  least 
to  indicate  that  the  felsite  broke  through  the  granitite,  and  the  absence  of 
Carboniferous  rocks  at  the  locality,  taken  in  connection  with  the  fact  that 
the  supposed  boundary  of  the  basin  passes  through  this  locality,  may  be 
interpreted  to  mean  that  the  felsite  flowed  out  upon  the  surface  of  the 
granitite  at  the  beginning  of  Carboniferous  deposition.  This  conclusion 
is  supported  by  facts  set  forth  on  page  155  concerning  the  felsites  of  North 
Attleboro. 


ACID  IGNEOUS  liOOKS.  117 

GRANITE-PORPHYRY. 

Granite-porphyry  occurs  in  the  northwestern  margin,  about  Diamond 
Hill  and  half  a  mile  northwest  of  Arnolds  Mills. 

This  latter  area  affords  a  tolerably  fresh  rock,  characterized  by  the 
presence  of  large  grains  of  quartz  and  orthoclase,  with  microscopic  garnet 
as  a  rare  accompaniment.  The  quartz  occurs  in  rounded  and  angular 
grains.  The  angulation  of  the  quartz  is  probably  in  part  due  to  a  move- 
ment of  the  magma  after  partial  cooling.  The  quartz  also  shows  embay- 
meuts  of  the  groundmass.  It  is  further  characterized  by  the  usually 
observed  fluid  inclusions,  with  gas  bubbles,  which  move  about  in  the  cavi- 
ties. Some  of  these  bubbles  simply  change  their  position  with  reference 
to  gravity  when  the  slide  is  turned  up  or  down;  others  keep  up  a  contin- 
ual oscillatoiy  movement,  which  is  independent  of  the  accidental  jarrings 
due  to  the  manipulation  of  the  stage  of  the  microscope.  Magnetite  or 
ilmenite  is  present.  Apparently  the  iron  ores  of  the  granite-porphyries  of 
this  district  tend  to  form  aggregates  having  the  external  grouping  of  den- 
dritic minerals.  Chlorite  is  present  in  the  groundmass,  as  are  also  small 
crystals  of  hornblende.  Garnet  occurs  in  isotrojDic  sections  with  a  trian- 
gular outline,  a  pinkish  tinge  in  plain  light,  and  witli  traces  of  cleavages. 
Concerning  the  interpretation  of  these  porphyry  stocks,  see  page  155. 

OTHER   ROCKS. 

Farther  south  are  bosses  of  hornblende  rock  which  break  through  the 
Blackstone  series  This  is  a  fine-grained,  dark-blue  rock,  evidently  of 
igneous  origin.  Under  the  microscope  it  shows  considerable  alteration. 
Hornblende  occurs  in  idiomorphic  crystals,  affording  basal  sections.  There 
is  a  great  deal  of  what  appears  to  be  secondary  hornblende,  shown  by 
its  lack  of  crystalline  outline.  Chlorite  is  abundantly  present  in  scaly, 
felty  aggregates.  Muscovite  exists,  probably  as  an  alteration  product  of 
one  of  the  original  feldspars.  Calcite  occurs  in  the  rock,  and  is  probably 
derived  from  a  lime-soda  feldspar.  The  idiomorphic  character  of  the  horn- 
blende crystals,  where  this  character  is  preserved,  the  nature  of  the  second- 
ary products,  and  the  fact  that  quartz  is  present,  probably  as  a  secondary 
product,  lead  to  the  opinion  that  this  rock  was  originally  a  diorite  charac- 
terized by  little  or  no  free  quartz,  the  quartz  now  visible  having  been 
derived  by  the  breaking  up  of  the  bisilicates. 


118  GEOLOGY  OF  THE  IS^ARRAGANSETT  BASIN. 

Diamond  Hill  is  a  mass  of  quartz  veins  probably  segregated  as  late  as 
the  period  of  the  Wamsutta  formation  of  the  northern  border.  The  quartz, 
as  shown  by  Dr.  Foerste's  studies,  is  mainly  developed  in  the  southern  part 
of  a  mass  of  granite-porphyry  having  a  superficial  extension  of  about  2 
square  miles. 

GABBRO    HILLS    OF    SHARON. 

An  elongated  lenticular  area  of  gabbro  with  diorite  occurs  in  the 
Wrentham-Hingham  granitic  uplift,  bordering  the  southern  side  of  the  Nor- 
folk County  Basin.  The  following  notes  are  from  a  description  of  tlie  rock 
hj  Messrs.  J.  R.  Finlay  and  H.  I.  Richmond,  jr.,  to  Avhom  I  am  indebted  for 
the  use  of  their  manuscript  report: 

From  North  Foxboro  to  Gantou  Juiictiou  there  is  a  heretofore  undescribecl  range 
of  hills  composed  almost  entirely  of  gabbro.  The  area  of  this  rock  is  7  miles  long  and 
its  greatest  breadth  about  2  miles.  The  highest  point  of  this  range  is  Moose  Hill, 
which  attains  an  elevation  of  5G0  feet.  Southwest  of  Foxboro  the  gabbro  extends  in 
disconnected  bosses  as  far  as  Wrentham. 

At  Foxboro,  Mansfield,  East  Foxboro,  and  Canton  there  are  large  ledges  of 
coarse,  light-colored,  hornblendic  granitite,  so  situated  as  practically  to  surround  the 
gabbro  on  at  least  three  sides.  In  the  gabbro  and  along  the  northern  side  are  frequent 
dikes  of  aplite.  The  outcrops  of  a  finegrained  granitite  along  the  northern  side  attain 
considerable  size.  Exactly  what  is  the  relation  of  this  finegrained  granitite  to  the 
coarser  granitite  which  covers  so  much  territory  to  the  southeast  can  not  be  determined 
in  the  field,  as  they  are  nowhere  in  contact. 

The  coarse-grained  granitite  is  found  in  several  iilaces,  as,  for  instance,  just  west 
of  Canton  Junction,  penetrating  in  an  intricate  manner  patches  of  crystalline  schist. 
.In  the  railroad  cut  just  north  of  the  station  at  Canton  Junction  there  is  a  large 
exposure  of  coarse-grained  hornblendic  granitite,  while  south  of  the  station  and  just 
east  of  the  gabbro  is  a  large  area  of  biotite-granitite.  Adjoining  these  rocks  to  the 
south  and  east  is  the  light-colored  coarse  granitite  of  the  region.  South  of  Canton 
Junction,  a  mile  east  of  the  railroad,  there  is  a  large  boss  of  diorite  which  has  burst 
through  the  granitite.  Blocks  of  coarse-grained  granitite  are  inclosed  in  the  diorite. 
Between  the  diorite  and  the  gabbro  is  a  strip  of  granitite  a  quarter  of  a  mile  wide. 

The  coarse  granitites  aie  older  thau  the  diorite,  but  are  younger  than  the  schists 
at  Canton  Junction.  The  gabbro  is  older  thau  the  fine-grained  granitite  dikes  pene- 
trating its  mass,  but  their  relation  to  the  coarse  granitites  is  unknown.  The  youngest 
rock  of  the  region  is  a  diabase,  which  is  found  in  dikes  cutting  the  other  rocks. 

A  petrographical  study  of  the  gabbro  showed  variations  to  a  dioritic  phase.  The 
diorite  exists  in  certain  areas  in  the  gabbro. 


CHAPTER    IV. 

THE  CARBONIFEROUS  BASIN. 

The  rocks  referred  to  the  Carboniferous  period  in  the  Narragansett 
Basin  are  grouped  together,  either  for  the  reason  that  they  are  known  to 
contain  the  fossils  pecuHar  to  this  period  or  because  they  are  stratigraph- 
ically  united  with  those  which  are  thus  fossiliferous.  The  members  of  the 
formation  are  arkoses,  conglomerates,  sandstones,  shales,  and  coals,  with  a 
great  variety  of  secondary  structures.  The  strata  are  almost  everywhere 
bent  into  steep-sided  folds.  Limestones  and  rocks  of  igneous  origin  are 
conspicuous  only  in  certain  parts  of  the  area.  The  beds  are  nonmarine, 
and  present  no  signs  of  equivalency  in  their  lower  strata  with  the  lower 
Carboniferous  or  Mississippian  series. 

In  a  geiaeral  way  the  strata  of  the  basin  exist  under  two  phases:  One 
is  a  belt  of  much  metamorphism,  beginning  near  Pawtucket  and  extending 
southward  and  widening  to  the  sea  in  Narragansett  Bay,  but  most  pronounced 
along  the  western  boundary  (see  fig.  6,  p.  120).  The  second  phase  is  char- 
acteristic of  the  greater  portion  of  the  remainder  of  the  area,  or  about  two- 
thirds  of  the  whole,  extending  eastward  and  north  into  the  Norfolk  County 
Basin.  In  this  field  the  effects  of  metamorphism  are  rarely  so  great  as 
seem  commonly  to  be  believed  by  geologists.  The  transition  between  the 
two  fields  is  often  very  abrupt.  The  geologist  who  should  pass  from  the 
nearly  vertical  metamorphic  strata  of  the  East  Side  in  the  city  of  Provi- 
dence, Rhode  Island,  to  the  slightly  folded  and  unaltered  sandstone  and 
shale  beds  of  East  Providence,  would,  from  a  comparison  of  the  rocks 
alone,  be  led  to  infer  that  there  was  in  this  field  a  set  of  very  ancient  tilted 
rocks  flanked  on  the  east  by  strata  of  much  less  antiquity.  So  short  is  the 
space  between  the  two  rock  phases  at  this  point,  being  the  width  of  the 
Seekonk  River  only,  that  one  is  led  to  believe  that  an  intermediate  zone 
of  considerable  width  has  been  concealed  by  a  fault. 

In  the  less  metamorphosed  area,  with  which  this  part  of  the  report  has 


120 


GEOLOGY  OF  THE  NAEEAGANSETT  BASIK 


mainly  to  do,  the  acquisition  of  secondary  characters  in  the  strata  is  very 
closel}^  related  to  the  degree  of  tilting  which  they  have  undergone.  Aside 
from  one  or  two  narrow  belts  of  dynamic  metamorphism,  accompanied  by 
the  development  of  new  minerals,  the  alteration  is  generally  limited  to  the 
production  of  cleavages  and  joint  structures.  It  is  on  account  of  this  lesser 
degree  of   alteration  and  the  identifiable  condition  of  plant  remains  that 


Fig.  6, — Map  showing  distiibution  of  metamorphosed  Carboniferous  rocks. 
A,  Narragansett  Bay  area  of  maximum  metamorpliism ;  B,  Winueconnet  area ; 
C,  Morrill's  area  in  Norfolk  County  Basin. 

this  portion  of  the  field  affords  the  best  ground  in  the  Carboniferous  basin 
for  determining  the  succession. 

In  the  subsequent  pages  the  attempt  to  establish  certain  rock  g-roups 
in  a  typical  area  will  be  followed  by  a  description  of  the  extension  of  the 
rocks  over  the  remaining  field.  Before  describing  the  rocks,  however,  I 
shall  discuss  the  facts  relating  to  the  general  structure  and  the  boundary  of 
the  basin. 


THE  CARBONIFBEOUS  BASIN, 


121 


GENERAL  STRUCTURE  OF  THE  BASIN. 

The  broader  secondary  features  of  the  basin — the  system  of  folds  with 
their  axes  and  the  parallel  direction  of  the  borders — are  relatively  simple. 
The  structural  outline  of  the  basin  is  that  of  a  ship's  knee,  with  the 
ang'le  on  the  northwest,  one  arm  extending  southward  to  the  mouth  of 
Narragansett  Bay,  the 
other  eastward  toward 
Cape  Cod  Bay,  and  the 
inner  curve  forming  the 
border  from  Tiverton 
northeastward  to  Lake- 
ville.  If  a  line  be  drawn 
from  the  northwestern 
corner  near  Diamond 
Hill  (see  fig.  7)  south- 
eastward to  a  bisection 
of  the  curvilinear  border 
near  Fall  River,  it  will 
pass  through  the  three 
deep  synclinal  depres- 
sions in  which  the  upper- 
most conglomerates  of 
the  Carboniferous  have 
been  infolded  and  23re- 
served  from  denudation. 
On  the  northwest  this 
line  also  passes  through 
the  small  area  of  pro- 
found dislocation  and  FicT.—lIap  showing  general  outline  of  the  Narragansett  Basin.  A-B,  line  pass- 
ing througli  deeper  synclines  of  middle  of  the  area;  aa,  inlier  of  granitite  and 
uplift  which    brings    the  Cambrian  at  HopplnHUl  and  the  Diamond  HiII  quartz  mass  on  western  border^ 

,  .  bb,  granitic  and  gnelssie  inliers  near  Bristol,  Rhode  Island;  CO,  synclines  with 

granitite     Ol      Xi  O  p  p  l  n  coarse  conglomerates ;   oo,  synclines  along  northern  border  of  the  basin ;  dd, 

.^-j.,-,,      1         /-.  1      .  -I  gneiss  structure  in  New  Bedford  area- 

Hill,  the  Cambrian,  and 

the  lower  Carboniferous  strata  to  the  surface.  West  of  this  line  the  strikes 
trend  nearly  north  and  south;  east  of  the  line  they  trend  about  east  and 
west.      This    axis   of   pressure,  moreover,  appears    to    have    been    that  in 


122 


GEOLOGY  OF  THE  NAERAGANSETT  BASIN. 


-;--  i 


■hk 


/  s,/ 


which  powerful  thrusts  have  acted  on  the  region 
to  the  southeastward.  The  granitite  of  the  south- 
ern border  in  the  region  of  this  axis,  notably 
about  Fall  River,  is  sheared  and  rendered  locally 
schistose  by  reason  of  the  pressure  to  which  it  has 
been  subjected. 

If  we  continue  this  line  .still  farther  southeast- 
ward, it  will  be  observed  that  the  gneisses  of  the 
5  New  Bedford  area  exhibit  structures  roughly  con- 
ii  centric  to  the  Carboniferous  strikes  on  the  north- 
I  west  (see  dd,  fig.  7).  The  whole  array  of  structures 
»  points  to  an  older  land  mass,  now  submerged,  which 
I  lies  in  this  southeastern  versant  of  the  New  England 

0  coast.     From  this  area  the  deposits  of  later  times, 

1  wrapped  about  its  northern  and  western  sides, 
1.  appear  to  have  been  pressed  toward  the  northwest. 
g  The  southern  arm  of  the  basin  is  parallel  in 

structure  with  the  strikes  of  southern  New  England 
I  westward  to  the  Taconic  range.  The  eastern  arm 
I  of  the  basin  coincides  in  trend  with  the  Norfolk 
s  County  and  Boston  basins  in  their  eastern  parts. 
g  These  last-named  show  also,  in  their  inner  western 
I  extensions,  the  tendenc}^  to  become  concentric  with 
g  reference  to  a  point  on  the  southeast. 
g  The  number  of  great  folds  in  the  basin  is  few 

I  (see  figs.  8  and  9).  Along  the  line  above  referred  to 
»  there  are  probably  not  more  than  four  great  syn- 
£  clines  and  three  intervening  anticlines.  None  of 
these  folds  appear  on  earlier  sections  of  this  basin 
(see  fig.  10).  The  great  mass  of  sediments  is  here 
thrown  into  folds  having  dimensions  quite  equal  to 
those  of  the  Appalachian  folds  in  Pennsylvania  (see 
fig.  8).  From  axis  to  axis  of  the  same  kind  is  a  dis- 
tance upward  of  6  miles  (see  map,  fig.  7).  With 
dips  often  of  45°  or  more,  folds  of  so  great  a  breadth 
are  commensurable  only  with  a  great  thickness  of 


STEDCTURE  OF  THE  BASIN. 


123 


strata,  of  which  there   can  not  be  less  than  12,000  feet  now  remaming. 
East  of  this  Hne  the  upper  strata  are  apparently  denuded  and  the  structure 


Fig.  9.— Outline  map  and  general  cross  section  of  the  basin. 


is  less  well  shown  (see  fig.  8),  lai-gely  owing  to  the   covering  of  glacial 
drift.      In   the   southern  arm,   as  is   shown  in  Dr.   Foerste's   report,  like 


changes  have  taken  place,  and  the  incursion  of  the  sea  has  done  that  which 
is  performed  by  sheets  of  sand  and  gravel  in  other  parts  of  the  basin. 


124  GEOLOGY  OF  THE  NAERAGANSETT  BASIN. 

MAPS  OF  THE  BOUNDARY  OF  THE  BASIN. 

The  progress  in  knowledge  of  the  geology  of  this  district  is  very  Avell 
represented  by  the  delineation  of  the  boundaries  of  the  Carboniferous 
formation  on  maps  since  the  time  of  Maclure.  In  his  map  of  1817  this 
field  of  rocks,  then  called  "Transition,"  is  represented  as  a  triangular  area, 
with  the  base  on  the  eastern  shore  of  Narragansett  Bay,  between  Providence 
and  Westport  Harbor,  and  the  apex  at  Boston. 

The  first  official  surveys,  those  of  Hitchcock  in  Massachusetts  and 
Jackson  in  Rhode  Island,  the  final  maps  of  which  were  published  in  1841 
and  1840,  respectively,  gave  the  boundaries  as  they  have  been  commonly 
represented  on  compiled  maps  up  to  the  present  time.  Dr.  C.  T.  Jackson's 
map  of  1840  represents  the  boundary  in  Rhode  Island  with  much  accu- 
racy, but  a  strip  of  the  more  highly  metamorphosed  beds,  in  Cumberland 
on  the  north  and  in  Kingston,  South  Kingston,  and  the  southern  part 
of  Jamestown  on  the  south,  is  included  in  his  group  of  "primary  rocks," 
as  are  also  the  basal  members  of  the  Carboniferous  along  the  Fall  River 
shore. 

Edward  Hitchcock's  map  of  1841  gives  the  outlying  boundary  of  the 
Carboniferous  with  much  fidelity,  but  the  shoulder  angles,  probably  due  to 
cross  faults,  along  the  northern  border  are  not  shown.  Owing  to  his  belief 
in  the  Devonian  age  of  the  red  strata  in  the  northwestern  part  of  the  field, 
an  attempt  was  made  to  draw  a  line  between  these  beds  and  the  Coal 
Measures.  No  attempt  is  made  to  show  the  inliers  of  granitic  and  other 
rocks  in  North  Attleboro  and  Namasket;  indeed,  they  are  nowhere  described 
by  him. 

A  later  map,  entitled  Bristol  and  Rhode  Island  Coal  Field,  published 
in  1853,^  represents  Devonian  rocks  as  lying  in  a  belt  along  the  western 
border  of  the  basin  from  Cranston  northward  into  the  Norfolk  County  Basin, 
and  as  sending  out  branches  near  Burnt  Swamp  Corner  eastward  along  the 
northern  border  of  the  main  basin  to  Foxboro  and  westward  toward  Belling- 
ham.  The  occurrence  of  the  Carboniferous  formation  along  the  Fall  River 
shore  is  not  5^et  recognized,  nor  are  the  outcrops  of  granite  at  Namasket 
and  North  Attleboro.  The  same  is  true  of  the  horseshoe  fold  of  the  red 
rocks  which  occur  in  North  Attleboro. 

'  Massachusetts  House  Document  No.  39,  March,  1853. 


BOUNDARY  OP  THE  BASIK  125 

Sir  Charles  Ly ell's  map  of  1845  is  fairly  accurate  as  regards  the 
boundaries  of  the  basin,  but  the  southern  half  of  the  Massachusetts 
extension  of  the  Carboniferous  is  erroneously  colored  to  represent  the  Old 
Red  sandstone,  or  Devonian.  The  connection  with  tlie  Norfolk  County 
Basin  is  not  shown.^ 

Sir  W.  E.  Logan,  in  the  geological  map  of  Canada,  dated  1864, 
accompanying  the  Atlas  of  1865,  represents,  on  the  authority  of  James 
Hall,  the  ou.tlines  of  the  Carboniferous  basin  and  its  connection  with  the 
Norfolk  County  Basin,  the  beds  of  which  latter  field  are  for  the  first  time 
colored  as  Carboniferous. 

C.  H.  Hitchcock  published  a  map  in  1871  in  which  a  barrier  of 
granitic  rocks  between  the  red  beds  of  the  Narragansett  Basin  and  the 
Norfolk  Basin  is  again  erroneously  introduced.  Other  changes  in  the  west- 
ern boundary  are  made  by  i-eferring-  a  belt  of  strata  to  the  Silurian. 

W.  O.  Crosby's  map  of  1877  gives  a  generalized  boundary  of  the 
northern  part  of  the  basin,  and  an  attempt  is  made  to  show  the  connection 
between  the  NaiTagansett  and  Norfolk  County  basins.  The  Carboniferous 
is  shown  extending  as  a  tongue  northward  to  Norwood  in  the  Norfolk 
County  Basin,  the  underlying  beds  being,  on  the  authority  of  Edward 
Hitchcock,  represented  as  Devonian. 

In  1880  Crosby  and  Barton  published  an  account  of  their  tracing  the 
beds  of  the  Norfolk  County  Basin  into  the  Nairagansett  Basin,  and  stated 
their  reasons  for  considering  all  the  beds  to  be  Carboniferous,  but  they  did 
not  publish  a  map. 

The  latest,  compiled  general  geological  maps  of  the  United  States^ 
perpetuate  the  error  in  regard  to  the  nature  of  the  connection  between  the 
Norfolk  and  Narragansett  basins,  a  bond  which  was  correctly  shown  on 
Logan  and  Hall's  map  of  1864,  and  still  earlier  under  the  coloring  of 
Devonian  in  the  Hitchcock  map  of  1841. 

BOUNDARY    OF    THE    BASIN    ON    THE    KOETH    AND   EAST. 
From  Cranston  to  the  Blackstone  River. In  tho   SOUtllWeSt   COmCr  of   tllO   PrOvidcUCe 

quadrangle  the  basal  beds  of  the  Carboniferous  are  seen  standing  in  nearly 
vertical  attitude  against  the  boundary  wall  of  the  pre-Carboniferous  series. 

■  Travels  in  North  America,  Vol.  II,  New  York,  1845,  PI.  II. 

=^C.  R.  Van  Hise,  after  McGee  and  Hitchcock:  Bull.  U.  S.  Geol.  Survey  No.  86,  PI.  XI.  W.  J. 
McGee:  Fifth  Ann.  Kept.  U.  S.  Geol.  Survey,  1884,  PI.  II. 


126  GEOLOGY  OF  THE  IS^AERAGANSETT  BASIN. 

The  angular  fragments  of  the  pre-Carboniferous  rocks  contained  in  these 
beds,  together  with  the  meridional  strikes  of  the  Carboniferous  as  con- 
trasted with  the  nearly  east-west  strikes  of  the  older  clastic  series,  afford 
abundant  evidence  of  the  unconformity.  The  exact  contact  is  not  shown. 
North  of  this  locality  the  Carboniferous  beds  do  not  appear  clinging  to  the 
escarpment  above  the  level  of  the  glacial  sand  plains.  In  succession  along 
this  escarpment,  granite,  gneiss,  schists,  and  quartzite  come  up  to  the  plane 
of  the  base  of  the  Carbonifei-ous,  indicating  the  varied  lithological  character 
and  structure  of  the  floor  on  which  the  sediments  were  laid  down  along 
this  western  border.  Direct  evidence  of  faulting  is  wanting.  For  most  of 
the  distance  the  lowest  and  nearest  visible  outcrops  of  the  Carboniferous 
are  from  2,000  to  3,000  feet  eastward  of  the  line,  and  probably  at  approxi- 
mately that  distance  above  the  base  of  the  series.  Throughout  this  section 
a  distinct  valley  exists  along  the  contact;  its  western  wall  is  formed  by  the 
escarpment  of  pre-Carboniferous  rocks,  including  some  Carboniferous  beds 
lying  to  the  west  and  forming  a  part  of  the  escarpment  at  the  point  of 
beginning;^  its  eastern  wall  is  formed  by  a  broken  ridge  of  hard  sandstones 
which  stand  up  to  the  level  of  the  adjacent  peneplain  developed  on  the 
crystalline  area  to  the  westward.  This  ridge  is  broken  through  at  Cranston 
and  Olneyville;  and  in  each  case  the  gap  is  opposite  a  valley  opening 
eastward  out  of  the  crystalline  area.  The  deep  reentrants  in  the  pre- 
Carboniferous  rocks  are  thus  shown  to  be  of  a  date  later  than  the  Carbon- 
iferous period  and  in  no  waj  affect  the  boundary  line  by  their  having 
been  originally  filled  with  sediments.  On  the  assumption  that  the  peneplain 
is  of  Jura-Cretaceous  age,  the  denudation  of  the  Carboniferous  soft  rocks 
below  that  level  is  an  index  of  Eocene  and  later  erosion,  and  these  valleys 
along  and  across  the  contact  are  post-Cretaceous.  The  cross  valleys  are 
not  of  glacial  origin;  the  movement  of  the  ice  was  nearly  at  right  angles 
to  their  course.  The  same  remarks  concerning  the  age  of  topographic 
features  apply  to  the  valley  of  the  Blackstone,  the  course  of  which  is  else- 
where described  in  this  report.  It  suffices  to  state  here  that  it  turns  from 
a  southeast  to  a  south  course  immediately  on  entering  the  basin. 


'Ill  tracing  the  boundaries  of  the  rocks  lying  on  the  western  boundary  of  the  Narragansett 
Basin,  Mr.  J.  H.  Perry,  of  the  United  States  Geological  Survey,  has  recently  shown  that  metamorphic 
Carboniferous  aikoses  ami  conglomerates  occupy  a  small  area,  about  half  a  mile  wide,  lying  to  the 
west  of  the  boundary  as  drawn  by  Dr.  Foerste  and  myself  where  our  maps  join. 


BOUNDARY  OF  THE  BASIN.  127 

From  the  Blackstone  River  to  Sheldonville. TlirOUgllOUt    tllls      nOrtliem     half    of    tllB 

western  boundaiy  actual  contacts  of  the  Carboniferous  upon  the  underlying 
rocks  have  not  been  seen.  North  of  the  Blackstone  RiA'^er  the  NW.-SE. 
strikes  of  the  Blackstone  series  can  be  traced  to  within  short  distances  of 
the  NE.-SW.  strikes  of  the  Carboniferous  beds,  indicating  from  the  angle 
which  the  latter  make  with  the  western  boundary  that  they  have  probably 
been  faulted.  From  Millers  River  northward  a  boundary  valley  continues 
as  far  as  Diamond  Hill.  In  the  Millers  River  section  gray  basal  conglomer- 
ates dip  off  eastward  at  steep  angles,  but  the  valley  is  wholl}'  excavated 
in  the  Carboniferous  rocks.  Northward,  in  the  Thompsons  Hill  area,  the 
Coal  Measures  come  in,  apparently  by  downfaulting  along  the  border. 
From  Diamond  Hill  to  Joes  Rock,  seen  on  the  Franklin  atlas  sheet,  the 
Carboniferous  rocks  are  in  unconformable  relation  with  the  lower  Cam- 
brian red  shales,  but  details  of  this  relation  are  wanting. 

Connection  between  the  Narragansett  and  Norfolk  County  basins. At   SheldoUvillc  tlie   rOck 

of  the  Narragansett  Basin  can  be  traced,  as  stated  by  Crosby  and  Barton 
in  1880,  into  the  southwestern  end  of  the  Norfolk  County  Basin,  through 
a  pass  not  exceeding  2,500  feet  in  width  between  walls  of  the  hornblende- 
granitite.  The  hornblende-granitite  comes  up  to  this  stratigraphic  isthmus 
with  nearl}^  rectangular  corners,  as  shown  in  the  map,  fig.  7  (p.  121).^ 

Sheldonville  cross  fault. — Tlie  most  reasouablc  explanation  of  the  rectangular 
boundaries  of  the  Carboniferous  and  granitic  rocks  at  this  point  is,  as  sug- 
gested by  Mr.  J.  R.  Firday,  the  occurrence  of  a  fault  passing  in  a  NNW.- 
SSE.  direction.  This  view  is  confirmed  by  the  extensive  faulting  of  the 
Carboniferous  beds  southward  through  Plainville  in  the  same  direction,  as 
Mr.  Finlay  has  amply  demonstrated  in  the  field. 

Actual  fault  contacts  in  the  Sheldonville  pass  have  not  been  seen. 
There  is  an  outcrop  of  red  sandstone  striking  NE.  and  dipping  60°  N.  in 
the  pass  in  the  western  granitic  corner,  very  close  to  the  supposed  fracture. 

From  Sheldonville  to  Foolish  Hill.— From  ucaT  Bumt  Swiiuip  Coruer  eastward  the 
boundary  can  be  fixed  with  approximate  exactness.  Messrs.  L.  S.  Griswold 
and  C.  F.  Marbut  have  determined  the  relations  of  the  rocks  at  a  number 


'  Some  of  the  earlier  geologists  supposed  that  the  Ehode  Island  and  Worcester  areas  are  con- 
nected through  the  Blackstone  Valley,  but  Prof.  Edward  Hitchcock  showed  that  these  areas  are 
separated  by  a  wide  district  of  gneiss.  Dana,  Manual  of  Geology,  3d  ed.,  1880,  p.  319.  Hitchcock, 
Final  Report  on  Geology  of  Massachusetts,  1841. 


128  GEOLOGY  OF  THE  NAREAGANSETT  BASIN. 

of  points  as  far  east  as  Brockton.  The  basal  series  of  the  Carboniferous 
may  be  seen  within  a  few  feet  of  contact  with  the  g-ranitite  in  Wrentham, 
in  the  low  hill  half  a  mile  north  of  the  Shepardville  reservoir.  So  far  as 
can  be  observed,  the  strata  are  simply  downfolded  without  faulting.  Along 
this  line  there  is  little  topographic  expression  to  the  contact.  The  Carbon- 
iferous area  is  covered  by  a  low,  gently  undulating  drift  plain,  while  the 
granitic  rocks  rise  into  rounded  knobs  having  elevations  of  from  100  to 
200  feet  above  the  plain  on  the  south. 

Foolish  Hill  fault. — Midway  between  Foxboro  and  Mansfield  the  boundary 
line  makes  a  rectangular  turn  along  the  western  face  of  Foolish  Hill. 
This  side  of  the  hill  presents  a  long,  smooth  wall,  inclined  steeply  westward. 
The  basal  beds  of  the  Carboniferous  rise  up  on  the  southern  face  of  this 
granitic  hill,  with  steep  dips  to  the  southward,  and  reappear  on  the  low 
ground  to  the  westward  with  an  oflFset  of  2,000  feet  or  more  to  the  north. 
The  railroad  from  Mansfield  to  Foxboro  follows  approximately  the  line  of 
this  fault. 

From  Foolish  Hill  to  Brockton. — Eastward  to  Eastou  tho  coutact  can  be  traced 
with  less  certainty.  The  attitude  of  the  basal  Carboniferous  beds  on  the 
south  varies  as  regards  angle  of  dip  from  point  to  point,  but  is  generally 
much  steeper  as  the  contact  is  approached.  This  change  of  dip  is  so 
marked  in  some  cases  as  to  suggest  unconformity  between  the  red  basal 
series  and  the  overlying  gray  carbonaceous  beds.  While,  as  before  noted, 
no  actual  faulting  can  be  shown  in  these  cases,  it  may  be  questioned 
whether  the  steeper  dips  along  the  border  do  not  express  the  upward  drag 
of  the  edges  of  strata  from  downfaulting  of  the  rocks  in  the  basin. 

Between  Easton  and  Brockton  there  are  positive  indications  of  small 
faults  along  the  boundary,  shown  in  actual  exposures,  but  the  precise  nature 
of  the  disturbances  and  their  bearing  upon  the  form  of  the  basin  in  this 
region  are  not  clear  on  account  of  the  drift  coating. 

A  mile  northeast  of  the  last-named  locality  is  a  very  considerable 
irregularity  in  the  boundary,  by  which,  according  to  Messrs.  Griswold  and 
Marbu^t,  the  red  beds  in  vertical  positions  are  let  into  the  granitite  floor. 
Still  nearer  Brockton  the  sudden  disappearance  of  red  sandstone  in  the 
drift  for  a  space  indicates  a  displacement  or  disappearance  of  the  beds  by 
erosion.  The  fact  is  worth  noting  here  that  the  coarse  pink  granite  just 
south  of  Montello  railroad  station  is  faulted  along  NE.-SW.  planes. 


BOUNDARY  OF  THE  BASIN.  129 

In  the  course  of  grading  the  bed  of  the  Old  Colony  Railroad  from 
Brockton  northward,  since  the  field  work  for  this  report  was  finished,  Car- 
boniferous gray  sandstones  with  fossil  plant  stems  were  exposed,  according 
to  the  studies  of  Mr.  M.  L.  Fuller,^  for  some  distance  north  of  the  main 
boundary  line  on  either  side  of  that  city.  I  am  indebted  to  Mr.  Fuller  for 
information  concerning  the  boundary  as  drawn  on  the  accompanying  map. 

From  Brockton  to  North  River. — Outcrops  of  tlic  Stratified  rocks  here  become 
very  infrequent,  but  enough  are  exposed  to  define  the  approximate  position 
of  the  boundary. 

shumatuscacant  fault. — Betwceu  Brocktou  aud  Abington  there  are  angles  in 
the  border  which  indicate  the  existence  of  cross  faults,  one  in  the  path  of 
Beaver  Brook,  the  other,  and  more  unmistakable  case,  that  along  the  line 
of  the  Shumatuscacant  River  in  Abington.  By  this  latter  dislocation  the 
boundary  line  on  the  east  is  set  northward  for  the  distance  of  a  mile. 

Through  Rockland  and  thence  eastward  across  Hanover  to  the  north- 
east corner  of  the  basin,  the  boundary  can  be  delineated  only  by  drawing 
a  line  south  of  the  known  exposures  of  granite  and  north  of  the  first  appear- 
ance of  Carboniferous  rocks  in  the  drift.  The  valley  of  Third  Herring 
Brook  follows  the  boundary  for  a  short  distance,  and  the  North  River  takes 
an  eastward  turn  across  the  line. 

From  North  River  to  Lakeviue. — Aloug  tliis  llue  the  bouudary  is,  because  of  the 
drift  mantle,  not  accurately  known.  Granitite  appears  in  Namasket  about 
4  miles  west  of  the  line,  as  heretofore  represented  on  maps  of  the  basin, 
and  it  is  not  certain  that  this  outcrop  is  a  mere  inlier.  In  the  absence  of 
positive  information  on  this  point  it  is  tentatively  i-epresented  as  a  part  of 
the  eastern  granitic  area.  Between  North  Plympton  and  Halifax  the  basin 
is  also  made  to  include  an  area  of  felsites,  the  exact  limits  of  which  are' 
unknown.  The  protrusions  of  the  eastern  margin  into  the  basin  in  the  form 
of  felsite  in  Plympton  and  of  granitite  in  Middleboro  are  near  enough  to  the 
lines  of  anticlinal  axes  in  this  portion  of  the  basin  to  lend  support  to  the 
hypothesis  that  the  basement  of  the  Carboniferous  is  exposed  at  these  locali- 
ties by  the  folding  of  that  floor  in  conformation  to  the  structure  of  the  once 
overlying  strata.  If  this  view  be  correct,  we  should  expect  to  find  the 
lobate  areas  between  the  tongues  of  igneous  rock  forming  synclines  in  the 


'Anew  occurrence  of  Cr-vboniferous  fossils  in  the  Narragansett  Basin:  Proc.  Boston  Soc.  Nat. 
Hist.,  Vol.  XXVII,  1896,  pp.  195-199. 
MON  XXXIII 9 


130  GEOLOGY  OF  THE  NAERAGANSETT  BASIN. 

Carboniferous.  The  single  but  pronounced  meridional  strike  of  the  outcrop 
near  Judson  post-office  proves  that  the  Great  Meadow  Hill  syncline  does 
not  extend  to  the  eastern  margin,  and  we  are  led,  therefore,  to  infer  that 
other  synclines  exist  in  this  heavily  drift-covered  region.  The  east-west 
strikes  of  the  Carboniferous  in  Hanover,  where  they  are  in  close  proximity 
to  the  border  running  north  and  south,  make  it  almost  necessary  to  suppose 
that  there  has  been  faulting  along  this  line.  Granite  of  a  euritic  texture 
occurs  south  of  Plympton,  setting  an  eastern  limit  to  the  Carboniferous,  and 
there  is  thus  no  evidence  to  show  that  the  Carboniferous  extends  toward 
Cape  Cod  Bay  east  of  the  line  drawn  on  the  map. 

In  the  Furnace  Pond  area  reliance  has  been  placed  upon  the  distribu- 
tion of  the  glacial  drift,  the  incoming  of  granitic  blocks  in  large  quantities 
being  taken  as  the  approximate  northern  position  of  the  granitite  on  the 
south  of  the  basin.  The  line  across  the  lakes,  in  Lakeville,  is  wholly 
conjectural,  but  is  confirmed  by  the  position  of  granitite  exposures  three- 
fourths  of  a  mile  southwest  of  Elders  Pond. 

From  Lakeville  to  Steep  Brook. — Froui  tlic  viciulty  of  Myricks  soutliwestward 
the  contact  begins  to  take  on  a  topographic  expression  and  is  marked  by  an 
ice-worn  granitic  escarpment,  at  the  foot  of  Avhich  runs  the  Assonet  River. 
Just  south  of  Myricks  the  vallej^  of  Swamp  River  breaks  through  the 
granitite  and  is  taken  advantage  of  by  the  New  Bedford  branch  of  the  Old 
Colony  Railroad.  In  Freetown  the  granitite  is  exposed  in  Washington 
Mountain  and  near  Break  Neck  Hill.  Finally,  at  Steep  Brook,  seen  on 
the  Fall  River  sheet,  the  basal  arkoses  and  conglomerates  are  found  resting 
on  the  granitite  and  dipping  off  northwestward  at  an  angle  of  45°. 

INLIERS. 

In  addition  to  the  facts  regarding  tlie  outlying  boundary  of  the  Car- 
boniferous, a  few  statements  may  be  made  concerning  the  contact  of  the 
formation  with  the  inliers  which  have  been  noted  in  this  jjortion  of  the 
basin.  Inliers  are  conspicuous  features  on  Newport  Neck,  Conanicut  Island, 
and  in  the  region  about  Bristol,  for  a  description  of  which  the  reader  is 
referred  to  Dr.  Foerste's  section  of  this  report. 

There  is  only  one  definitely  determined  inlier  in  this  northern  part  of 
the  basin — that  of  Hoppin  Hill,  in  North  Attleboro — though  it  is  possible 
that  there  are  others,  as  at  Namasket  and  in  tlie  Cambrian  locality  near 
Diamond  Hill. 


BOUND AKY  OF  THE  BASIN.  131 

North  Attieboro  iniier. — 111  tlie  Novtli  AttleboFO  inlier  (see  PI.  XXIX,  in  Part 
III),  actual  contacts  of  the  Carboniferous  with  the  subjacent  Cambrian  and 
granitite  are  not  exposed,  but  the  evidence  points  to  the  unconformable 
relation  of  th<j  Carboniferous  and  Cambrian  strata. 

Namasket  granitite  area. — Horiiblende-granitite,  similar  to  the  rock  of  the 
northern  border  of  the  basin,  appears  in  a  low  outcrop  about  60  feet  above 
the  sea  in  the  village  of  Naraasket,  in  the  town  of  Middleboro.  The  expo- 
sure by  the  roadside  is  upward  of  200  feet  in  length,  and  is  at  a  distance  of 
3^  miles  from  the  nearest  granitite  outcrops  to  the  southeastward.  The 
nearest  visible  stratified  rocks  are  2  miles  south,  and  nothing  is  known 
reo-arding  the  contact.  It  is  not  at  all  improbable,  as  above  stated,  that  the 
exposure  of  granitite  at  this  point  marks  an  anticlinal  structure  in  the  Car- 
boniferous by  which  a  tongue  of  the  granitite  protrudes  into  the  basin  from 
the  eastern  border,  as  does  the  long,  broad  area  from  Hingham  westward  to 
Sheldonville,  separating  the  Narragansett  from  the  Norfolk  County  Basin. 

SUMMARY. 

The  boundary  in  this  northern  part  of  the  field  appears  to  be  inainly 
one  of  downfolded  beds  where  the  line  extends  east  and  west.  Down- 
faulting  is  suggested  only  where  the  line  runs  north  and  south.  Corre- 
lated with  this  evidence  is  the  presence  of  arkose  along  the  east-west 
borders,  and  its  almost  complete  absence  along  north-south  lines  in  the 
upper  part  of  the  basin.  These  faults  are  parts  of  a  series  which  appear  on 
the  east-west  boundary  lines  as  cross  faults. 

The  type  of  fault  crossing  the  boundary  of  the  basin  is  repeated  a 
number  of  times  along  the  northern  border.  These  cross  faults  along  the 
northern  margin  do  not  clearly  arise  out  of  the  physical  conditions  engen- 
dered at  the  contact  of  two  terranes  so  unequally  acted  upon  by  stress,  but 
rather  they  are  regional  dislocations  arising  in  the  pre-Carboniferous  ter- 
rane,  their  existence  being  clearly  brought  out  by  the  rectangular  notches 
which  they  introduce  into  the  boundary  line.  Outcrops  are  wanting  to 
show  how  far  these  faults  affect  the  beds  in  the  basin  above  the  lowermost 
strata.  Even  if  the  faults  were  limited  to  the  granitite  and  the  beds  imme- 
diately at  the  base,  we  should  expect  to  find  a  local  deflection  of  the  strike, 
in  the  form  of  a  flexure,  in  the  direction  of  the  offset  at  some  distance 
beyond  the  margin  of  the  fault  plane. 


1  32  GEOLOGY  OP  THE  NAERAGANSETT  BASIN. 

It  is  to  be  noted  that  the  faults  along  this  border  are  of  the  normal 
Basin  Range  type,  the  downthrow  being  in  blocks  on  the  east  and  west 
of  a  relatively  uplifted  block  in  Easton.  The  northward  recession  of  the 
boundary  east  and  west  of  this  block  is  in  accordance  with  this  structure. 
The  system  of  faults  is,  moreover,  transverse  to  the  Wrentham-Hingham 
uplift  of  igneous  rocks.  So  far,  however,  these  fractures  have  not  been 
traced  into  the  Norfolk  County  Basin.  The  throw  of  these  faults  is  not 
necessarily  great.  The  dip  of  the  strata  near  Brockton  and  Abington  is 
generally  low,  not  exceeding  15°,  and  the  surface  is  level,  so  that  a  ver- 
tical downthrow  of  1,420  feet  would  account  for  the  displacement  of  the 
boundary  1  mile  on  a  horizontal  plane  at  the  latter  place. 

The  date  of  the  faults  is  not  in  most  instances  determinable.  They 
are  clearly  post-Carboniferous,  but  their  correlation  with  the  dislocations 
which  deformed  the  Newark  basins  along  the  Atlantic  coast  in  middle 
Mesozoic  times  has  not  been  proved. 


CHAPTER  y. 
THE  CARBONIFEROUS  STRATA. 

DETERMINATION   OF   HORIZONS  WITHIN  THE  BASIN. 

The  earliest  attempts  to  discriminate  horizons  within  the  limits  of  the 
basin  were  made  by  Edward  Hitchcock  in  the  northwestern  part  of  the 
area,  where,  on  lithological  grounds,  the  red  Carboniferous  beds  were 
referred  to  the  Devonian  period. 

Sir  Charles  Lyell,  in  1845,  mapped  as  Devonian  a  broad  band  of  strata 
extending  through  Rehoboth,  Swansea,  Taunton,  and  thence  to  the  eastern 
margin,  but  it  is  now  known  that  the  beds  so  mapped  are  Carboniferous- 
In  1871,  C.  H.  Hitchcock  mapped  a  small  area  in  the  southwestern  part  of 
Attleboro  as  belonging  to  the  "Quebec  group,"  and  a  strip  along  the  west- 
ern border  of  Rhode  Island  as  Silurian,  but  both  these  occurrences  are  now 
known  to  be  Carboniferous.  In  the  eai-lier  work  of  T.  Nelson  Dale  about 
Newport,  the  Carboniferous  and  earlier  strata  were  divided  into  Paleozoic 
groups  based  on  lithological  characters.  Beyond  these  incomplete  maps  no 
attempts  have  ever  been  made  to  exhibit  the  formations  which  have  been 
recognized  by  several  authors  as  forming  horizons  in  the  coal  basin. 

MEANS    OP    DETERMINING    SUPERPOSITION. 

The  means  of  determining  horizons  in  the  Carboniferous  rocks  of  the 
Narragansett  Basin  are  purely  physical.  As  yet  the  fauna  and  flora  of 
the  Carboniferous  beds  are  too  little  known  to  be  employed.  A  series  of 
basal  arkoses  overlain  or  replaced  from  point  to  point  by  simple  quartzose 
conglomerates  can  be  traced  fairly  continuously  about  the  margin,  and  may 
be  recognized  at  a  few  points  in  the  interior.  Above  these  is  a  great 
succession  of  conglomerates,  sandstones,  and  shales  with  coal  seams,  which 
are  rarely  traceable  for  more  than  a  few  miles.  The  formation  is  preemi- 
nently conglomeratic. 

In  the  main,  reliance  has  been  placed  on  matching  strata  on  opposite  sides 
of  anticlinal  and  synclinal  axes,  checking  these  observations  by  gross  meas- 
urements of  thickness  and  by  observed  gradations  in  texture  and  thickness  of 
individual  beds.  The  results  can  be  said  to  be  little  more  than  approxima- 
tions. In  portions  of  the  area,  particularly  in  the  eastern  part  of  the  field,  a 
description  of  the  geology  can  deal  with  little  more  than  isolated  outcrops. 


134 


GEOLOGY  OP  THE  NARKAGANSETT  BASIN. 


I  am  of  the  opinion  that,  were  the  several  horizons  of  shales  explored 
for  fossils,  a  sufficiently  differentiated  flora  would  be  found  on  which  to 
base  a  more  satisfactory  subdivision  of  the  great  middle  series  of  sandstones 
and  shales  than  is  here  proposed  on  j^urely  physical  grounds. 

Tabular  vieto  of  the  strata  in  the  Narragansett  Basin. 


Northern  field. 

Southern  field. 

Group. 

Remarks. 

Local  areas. 

Characters. 

Local  areas. 

Characters. 

Dighton     (Cd) 

Rocky  "Woods  con  ■ 

Coarse    quartzile    and 

Purgatory 

Coarse  quartz- 

Probably,   though    not 

(1,000-1,500 

glomerate. 

granitic   pebble  con- 

conglomer- 

ite pebbles, 

certainly,  identical   in 

feet). 

glomerates,  with  finer 

ate. 

usually 

all  parts  of  the  field,  ly- 

Seekonk conglom- 

conglomerates     and 

much   elon- 

ing in  aynclines  above 

erate. 

sandstone. 

gated    and 
indented. 

the  Coal  Meaaares. 

Rhode    Island 

Westville    shales 

Alternations  of  fine 

Aquidneck 

Mainlyshales 

Both  the  Aquidneck  and 

Coal  Meas- 

and Seekonk 

and  medium  quartz,' 

shales    of 

with    coal 

Kingstown    series 

ures    (Cc) 

sandstones. 

quartzite,  and    gra- 

Dr.Foerste. 

beds. 

of  Dr.  Foerete,  when 

(10,000  feet). 

Tenmilo    RiTer 

nitic  pebble  conglom- 

traced northward,  ap- 

beds. 

erates,    with    pebbly 
sandstones,    sand- 
stones    (grauwacke), 

pear    to  form    equiva- 
lent  sections    beneath 
the     Dighton     group, 

Mansfield  beds. 

shales,  and  coal  beds, 

Kings  town 

Mainly    sand- 

one on  the  eastern,  the 

Cranston    beda, 

becoming     metamor- 

series    of 

stones    and 

other  on    the  western 

Sockanasset 

phic  southward. 

Dr.Poerate. 

conglom  e  r  ■ 

side    of    Narraffansett 

sandstones, 

Colors:    Black,    blue, 

ates    with 

Bay,  and  both  extend 

Pawtucket 

green,    gray,    locally 

coal  shales; 

downward  to  the  basal 

shales. 

red.       Odontopteris 

usually  met- 

beds    in    this    typical 

flora  and  insect  beds. 

aroorphic. 

area. 

"Wamsutta 

[slates 

Beds  of  quartz,  quartz- 

The Wamsutta  beds  are 

(Cw)  (1,000 

Wamsuttai    and 

ite,     felsites,    felaite 

not  traceable  south  of 

feet). 

[shales. 

breccias    and    felsite 

Providence ;    probably 

Attleboro  sand- 

conglomerates, sand- 

represented   by   lower 

stone. 

stones,     arkose,    and 

strata  of  Dr.  Foerste's 

"Wamsutta    c  o  n  - 

shales.     Colors:  Red, 

Kingstown  series.     In 

glomerates. 

locally    brown,    and 
green.     Calamites. 

the  vicinity    of   Paw- 
tucket the  Coal  Meas- 
ures   underlie    the 
Wamsutta. 

Pondville  (Cp) 

Millers  River  con- 

Quartz   conglomerates . 

Basa  beds. 

Quartzose 

Essentially  similar  prod- 

(100 feet). 

glomerates,  ar- 

Coarse,    white,    gra- 

conglomer- 

ucts   of   decayed    gra- 

kose beds. 

nitic  waste  or  arkose. 

ates    and 
arkose. 

nitic  land  surface  in  all 
parts  of  basin. 

TTn  com  form  ity. 

"Widespread  erosion  interval,  representing 
Cambrian. 

all  of  Silurian  and  Devonian 

time  and  probably  upper 

Pre  -  Carbonif- 

Broad  exposures  of  granitite  intruded  into 

Same  as  in  northern  field. 

Pre-Carboniferous  strata 

erouB. 

lower    and    middle    Cambrian    and    pre- 

not   definitely   deter- 

Cambrian sediments. 

i 

mined;   Cambrian  or 
pre -Cambrian. 

BASAL  BEDS.  135 

foematio:n"s  bei.ow  the  coal,  measures. 

pondville  group, 
basal  aekose  beds. 

Along  the  northern  border  where  observations  can  be  made,  the  red 
rocks  of  the  Wamsutta  series  either  rest  directly  on  the  granitite  or  are 
separated  from  that  basement  rock  by  a  sheet  of  grayish  arkoses  and  quartz 
pebble  and  quartzite  conglomerates.  It  is  evident  that  the  first  appearance 
of  red  sediments  was  not  simultaneous  all  along  the  border,  but  that  it 
de^aended  upon  local  conditions,  such  as  the  debouchure  of  streams,  the 
230sition  of  headlands  or  bays  controlling  the  nature  of  local  shore-line 
deposits.  With  the  exception  of  the  few  places  where  the  red  sediments 
designated  as  members  of  the  Wamsutta  series  come  in  at  the  base,  there 
may  be  said  to  exist  a  horizon  of  sediments  not  of  red  color  underlying  the 
Wamsutta  and  bearing  in  the  nature  of  their  particles,  independently  of 
their  position,  every  evidence  of  being  a  basal  series.  These  rocks  appear 
not  only  beneath  the  red  strata  in  the  Narragansett  Basin,  but  also  in  a 
characteristic  section  in  the  western  part  of  the  Norfolk  County  Basin.  I 
shall  refer  to  the  exposures  of  these  basement  strata  in  the  few  localities 
where  they  may  be  studied  to  advantage. 

Foolish  Hill  exposures. — At  the  base  of  the  Carboniferous,  on  the  southern 
face  of  Foolish  Hill,  between  Mansfield  and  Foxboro,  basal  arkoses  are  well 
exposed;  but  here  thin  bands  of  red  slate  begin  to  make  their  appearance, 
a  few  feet  above  the  base. 

North  Attieboro  exposures. — In  thc  towii  of  Nortli  Attleboro,  on  Division  street, 
and  at  points  near  the  railroad  station  on  High  street,  there  are  broad 
exposures  of  a  gray  arkose  derived  from  the  disintegration  of  the  horn- 
blendic  granitite.  Similar  exposures  occur  east  of  the  town,  where  by 
folding  the  basal  series  are  brought  up  in  close-pressed  folds. 

Pierces  Pasture  in  Pondville,  Norfolk  County  Basin. TllC  clcareSt  exhibition  of  the  baSal 

beds  of  the  Carboniferous  is  to  be  found  in  the  Norfolk  County  Basin  near 
Pondville  Station,  on  the  Walpole  and  Wrentham  Railroad.  The  small 
area  known  as  "Pierces  Pasture"  exhibits  in  its  topography  much  of  the 
ruggedness  of  an  unglaciated  region,  insomuch  that  the  nearly  vertical  beds 
stand  out  in  ridges  where  hard  and  resisting,  or  sink  into  depressions  where 
soft  and  yielding.     The  almost  entire  absence  of  glacial  drift  from  the  area 


136  GEOLOGY  OF  THE  NAREAGANSETT  BASIN. 

is  due  to  its  having  been  covered  by  a  remnant  of  the  ice  sheet  whose  mar- 
ginal sand  plains  surround  the  field  on  the  east,  south,  and  west.  The 
Carboniferous  beds  rest  here. upon  the  grauitite  and  dip  off  steeply  to  the 
north,  in  the  form  of  a  closed  and  puckered  syncline  plunging  eastward, 
the  cross  section  of  which  structure  is  as  follows,  beginning  on  the  sovith : 

1.  A  small  kuob  of  horublendic  grauitite.  This  i)asses  by  almost  inseusible  grada- 
tious  into  arkose. 

2.  Alternatiug  beds  of  arkose  and  grits,  with  vein  quartz  pebbles,  occasional 
nodules  of  the  grauitite,  aud  shaly  partings. 

3.  Quartz-pebble  conglomerate,  with  sandstone  partings,  the  latter  holding  casts 
and  hollows  of  fossil  trees  from  a  few  inches  to  more  than  a  foot  in  diameter,  often 
closely  pressed  and  forming  a  mere  gash  with  an  ocherous  cellular  layer.  (The  fossils 
described  by  Crosby  and  Barton  in  1880  were  the  casts  of  this  locality.) 

4.  Eed  and  green  slates,  with  sandy  partings. 

5.  Fine  quartz-pebble  conglomerate  in  eastern  part  of  the  lot ;  wanting  in  the 
western  section. 

6.  Eed  and  green  slates,  like  4  above,  with  flattened  and  cylindrical  casts ;  and 
small  greenish  chloritic  kernels,  due  to  metamorphism. 

7.  Quartz-pebble  conglomerate,  with  sandstone  i^artings,  containing  casts  and 
molds  of  fossil  trees;  one  cast  12  feet  long  and  12  by  18  inches  in  diameter. 

Whole  section  250  to  300  feet  in  thickness. 

Northward  the  beds  are  concealed  beneath  a  swamp.  This  section  is, 
on  the  whole,  one  of  the  most  instructive  basal  sections  in  the  Carbonifer- 
ous field  of  Massachiisetts,  and  may  be  taken  as  typical  for  the  general 
history  of  the  beginning  of  sedimentation  in  the  main  basin. 

Absence  of  basal  granitic  conglomerates. It  is  a  UOtOWOrthy  faCt  that  whlle  thc  CntlrO 

Carboniferous  section,  amounting  probably  to  a  thickness  exceeding  12,000 
feet,  is  mainly  conglomeratic,  there  is  in  this  northern  half  of  the  main 
basin  no  widespread  basal  conglomerate  such  as  we  find  exactly  at  the 
base  of  many  sections  in  the  geological  record.  The  general  absence  of 
basal  conglomerates  and  the  presence  of  arkose  along  the  border  indicate 
clearly  the  condition  of  the  land  surface  from  which  the  earliest  sediments 
were  derived.  The  failure  to  produce  pebbles  of  the  original  rock  under 
the  first  attack  of  denudation  must  evidently  have  been  due  to  the  deep 
disintegration  of  the  granitic  terrane  whence  the  sediments  were  derived 
and  the  low  grades  of  streams.  By  the  disintegration  of  the  feldspar  and 
the  decay  of  the  iron-bearing  silicates  of  the  igneous  rock  the  crystalline 
ingredients  fell  into  the  state  of  coarse  sand,  and  in  this  form  the  superficial 
portion  of  the  granitite  was  removed  to  the  area  of  deposition.     It  was  only 


BASAL  BEDS.  137 

later,  as  a  result  of  renewed  uplift  of  the  land  or  of  the  deeper  intrenchment 
of  streams  and  the  incision  of  waves,  that  the  fresh,  undecomposed  granitite 
came  into  the  grasp  of  the  eroding  agents,  and,  breaking  up  along  planes  of 
fracture,  made  pebbles.  In  the  meantime,  there  were  portions  of  the  granitic 
terrane  which  did  not  disintegrate.  These  parts  were  the  quartz  veins  and 
nodular  segregations  of  quartz  in  pegmatites,  and  to  some  extent,  perhaps,  in 
dike  rocks,  which  remained  and  formed  pebbles.  It  is  owing  to  this  reason 
that  the  first  conglomerates  overlying  the  arkose  beds  are  composed  mainly 
of  quartz  pebbles.  The  considerable  mass  of  these  pebbles  gives  some  idea 
of  the  thickness  of  the  decomposed  granite  section  which  was  removed  at 
this  time.  In  any  section  of  the  neighboring  granitites  at  the  present  time 
the  volume  of  quartz  large  enough  to  form  pebbles  in  a  cubic  yard  of  the 
rock  is  relatively  very  small.  Large  and  thick  veins  occur  here  and  there, 
but  it  is  not  conceivable  that  more  than  1  per  cent  of  the  average  granitite 
mass  would  yield  quartz  pebbles.  It  is  evident,  tlaerefore,  that  a  very 
thick  section  of  rock  was  subjected  to  disintegration  and  removal  in  order 
to  form  a  bed  of  quartz  conglomerate  50  to  100  feet  thick.  How  much  of  the 
quartz  came  from  veins  in  sedimentary  formations  into  which  the  granitite 
doubtless  penetrated  can  not  be  known.  The  quartz  would  probably  be 
more  abundant  in  these  rocks  than  in  the  granitic  stock  itself.  That  the 
depth  of  granite  removed  to  form  these  ai'koses  and  quartz  pebbles  was 
great  is  also  indicated  by  the  coarsely  crystalline  texture  of  the  granitite 
along  the  border,  showing  that  the  parts  which  we  now  see  are  well  into 
the  interior  of  the  original  mass  and  not  near  the  contact  with  the  rocks  into 
which  the  granitite  was  intruded,  for  the  reason  that  at  the  contact  the 
granitite  would  have  cooled  down  more  quickly  and  thus  have  induced 
upon  its  crystals  a  more  minute  texture  than  exists  in  the  mass,  where 
cooling  went  on  more  slowly. 

Geographical  conditions  indicated  by  the  basal  arkose, Tlie    foriUatioU    of    beds    of  arkoSe, 

and  the  abundant  reasons  above  cited  for  believing  that  the  land  on  which 
the  Carboniferous  beds  were  laid  down  had  long  been  subjected  to  secular 
decay  and  leaching,  make  it  necessary  to  suppose  that  the  grades  of  the 
streams  were  too  low  for  the  removal  of  the  products  of  disintegration  as 
fast  as  they  were  formed.  The  site  of  the  basin,  which  appears  to  have 
undergone  depression  at  the  time  deposition  set  in,  must  have  been  pre- 
viously without  very  strong  contrast  with  the  surrounding  country,  except 


138  GEOLOGY  OF  THE  NARRAGANSETT  BASIN. 

SO  far  as  it  was  a  lowland  or  valley,  as  Professor  Slialer  supposes  it  to 
have  been.  That  a  long  period  of  erosion  or  nondeposition  had  closed  at 
this  time  is  abundantly  proved  by  the  marked  unconformity  of  the  Cai-bon- 
iferous  with  the  underlying  terranes,  this  great  stratigraphic  break  embrac- 
ing, as  above  noted,  all  of  Silurian  and  Devonian  time,  if  not  as  well  the 
upper  Cambrian  at  the  beginning  of  this  interval  and  the  lower  Carbonifer- 
ous at  the  close. 

Absence  of  iron  oxides  in  the  basal  arkose. — Tlie  prevailing  whltlsh  aud  grayish  hues 
of  the  basal  arkoses,  and  of  the  conglomerates  immediately  above  them,  are 
in  strong  contrast  to  the  often  vivid  reds  of  the  overlying  and  occasionally 
intercalated  Wamsutta  series  to  be  described  beyond.  This,  bleaching  of 
the  first  Carboniferous  sediments  appears,  like  the  coloring  of  the  Wamsutta 
beds,  to  have  taken  place  prior  to  transportation,  and  the  two  processes 
may  be  said  to  be  complementary  to  each  other.  The  granitites  along  the 
northern  border,  and  almost  everywhere  adjacent  to  the  portions  of  the 
basin  where  the  red  series  of  strata  occur,  are  strikingly  red  by  reason  of 
the  discoloration  of  one  of  their  feldspars.  This  reddening  is  probably  one 
of  the  results  of  alteration  through  atmospheric  decay,  but  it  is  difficult  to 
determine  when  this  change  in  the  feldspar  began  to  take  place  in  an  effec- 
tive way,  for  the  granitites  in  the  present  superficial  zone  have  at  least  twice 
been  exposed  to  meteoric  waters,  once  at  the  beginning  of  the  Carboniferous 
deposition,  when  the  shore  line  was  creeping  over  the  rock,  and  since  then 
when  the  Carboniferous  covering  was  swept  away  and  the  rocks  were  again 
bared  to  weathering.  It  is  hardly  possible  to  suppose  that  the  decay  which 
has  led  to  this  reddening  occurred  in  Carboniferous  time,  for  the  reason  that 
the  pebbles  of  granitite  found  in  the  conglomerates  of  the  red  Wamsutta 
series,  or  higher  up,  are,  so  far  as  I  have  observed  them,  never  I'ed  except  by 
absorption  of  the  red  paste  in  which  they  are  embedded.  The  most  reason- 
able supposition  which  I  am  able  to  advance  is  that  the  superficial  products 
of  weathering  previous  to  their  traiasportation  in  Carboniferous  time  were 
leached  of  their  iron  salts,  which  penetrated  downward.  The  first  transpor- 
tation of  detritus  affected  the  superficial  leached  layer,  and  thus  the  basal 
beds  came  to  be  white,  as  we  now  see  them.  When  erosion  had  stripped 
away  the  bleached  materials  at  the  surface,  it  reached  the  highly  discolored 
rock  beneath,  as  yet  very  imperfectly  disintegrated,  from  which  were  pro- 
duced the  red  beds  of  the  Wamsutta  series. 


BASAL  BEDS.  139 

Absence  of  carbonaceous  matter  along  the  northern  margin. AnOtliei"  faCtOl'  wllich  haS  glVeH 

free  play  to  the  interchanges  of  the  iron  oxides  above  mentioned  in  their 
effect  upon  the  color  of  the  rocks  is  the  very  general  absence  of  carbo- 
naceous matter,  or  coal  beds,  in  the  basal  series.  In  proportion  to  the 
amount  of  carbonaceous  remains  present  in  the  strata,  the  colors  due  to 
the  difFerent  states  of  iron  are  concealed. 

Extent  of  the  arkose  zone. — There  is  Tcasou  for  belle  viug  that  the  arkose  bed 
is  nearly  continuous  about  the  margin  of  the  basin,  and  that  its  disap- 
pearance is  due  to  faulting  or  to  original  local  conditions  which  prevented 
its  accumulation.  To  what  extent  the  sheet  of  arkose  extends  beneath  the 
basin  is  not  known,  as  the  rock  is  not  exposed  in  the  anticlinal  axes  in  the 
central  part  of  the  basin,  for  the  reason  that  erosion  has  not  there  cut 
down  to  the  base.  The  arkose,  together  with  the  associated  quartz  con- 
glomerates, wraps  around  the  tongue  of  granitite  and  associated  igneous 
rocks  which  form  the  Wrentham-Hingham  uplift  between  the  Norfolk  and 
Carboniferous  basins,  and  I  see  no  reason  why  the  Carboniferous  basal 
sediments  should  not  have  been  continuous  over  this  area,  so  as  to  unite  the 
two  sets  of  beds  in  the  present  distinct  basins.  Until  it  can  be  shown,  as 
Crosby  and  Barton  believed  in  1880,  that  the  arkose  and  higher  strata  on 
either  side  of  this  granitic  mass  were  derived  from  it  alone,  and  not  carried 
over  on  it  as  a  sheet  of  sediment  from  some  still  more  northern  area,  there 
seems  no  reason  for  accepting  the  view  that  this  anticlinal  ridge  rose  above 
the  general  level  in  Carboniferous  time.  There  are  no  general  facts  to  show 
that  the  arkose  was  carried  along  shore  by  currents  more  in  one  direction 
than  another.  If  anywhere  thicker  than  at  other  points,  the  arkose  is  proba- 
b\j  most  developed  in  North  Attleboro.  In  the  eastern  part  of  the  basin, 
and  generally  in  the  northern  and  eastern  portions,  there  are  many  sand- 
stones far  above  the  base  which  would  be  denominated  arkose,  but  they 
are  not  to  be  mistaken  for  the  mixture  of  quartz  and  feldspar  of  granitic 
aspect  which  makes  up  the  mass  of  the  basal  series.  This  arkose  in  some 
instances  differs  but  little  from  the  original  igneous  rock  whence  it  was 
derived,  except  for  the  solution  of  the  iron-bearing  silicate,  a  slight  tritura- 
tion of  the  grains,  and  the  intercalation  of  clearly  stratified  beds  or  occa- 
sional waterworn  quartz  pebbles. 


140  GEOLOGY  OF  THE  NARRAGANSETT  BASIN. 


SUPRABASAL   CONGLOMERATES. 


The  conglomerates  which  occur  near  the  base  along-  the  margin  of  the 
basin  are  not  precisely  basal  in  the  sense  in  which  that  word  finds  its  most 
exact  use.  At  a  few  points  conglomerates  actually  rest  upon  the  basement 
floor  of  granite,  but  they  more  usually  overlie  beds  of  arkose.  The  reason 
for  this  order  of  deposits  lies  in  the  fact,  before  noted,  that  the  granitic  land 
area  was,  in  the  beginning  of  Carboniferous  erosion  and  deposition  in  this 
field,  so  decayed  at  surface  that  pebble  making  did  not  go  on  until  the  layer 
of  disintegrated  granite  was  stripped  off.  It  is  in  full  accord  with  this  chem- 
ical preparation  of  the  sediments  that  we  find  the  first  conglomerates  i^revail- 
ingly  quartzose  and  composed  of  quartzite — rocks  which  do  not  yield  to 
atmospheric  decay  so  readily  as  the  granite.  On  account  of  this  sequence 
in  the  deposition — first  arkose,  and  then  conglomerate — the  term  supra- 
hasal  conglomerate  expresses  more  exactly  than  hasal  conglomerate  the 
nature  of  the  inferior  pebble  beds  in  the  Narragansett  Basin.  Of  these 
suprabasal  conglomerates  there  are  a  few  noteworthy  exposures  believed 
to  be  approximately  on  the  same  horizon.  The  beds  are  often  composed 
of  quartz  pebbles,  the  remnants  of  veins  in  the  granitic  border,  the  latter 
rock  occurring  less  abundantly  than  in  the  higher  conglomerates.  These 
beds  form  the  closest  analogy  to  the  typical  Millstone  grit  which  occurs  in 
the  basin,  and  the  following  locality,  being  typical,  has  been  chosen  for  the 
type,  although  the  relations  to  the  arkose  and  the  basement  rocks  are  better 
shown  elsewhere. 

Millers  River  conglomerate. — In  tlic  Valley  of  Millcrs  Rlvcr,  iu  Cumberland, 
Rhode  Island,  there  is  a  broad  exposure  of  conglomerate  beds  underlying  the 
red  Wamsutta  series.  In  this  gray  series  there  are  tlu-ee  or  four  thick  beds 
of  conglomerate  with  small  quartz  and  qnartzite  pebbles.  The  best  section 
is  exposed  on  the  farm  of  Mr.  James  A.  Miller.  The  thickness  is  here 
unusually  great,  being  as  much  as  300  to  400  feet. 

South  Attieboro  exposure. — Bctweeu  South  Attleboro  and  Lanesville,  in  the 
triangular  area  between  the  southern  end  of  the  great  horseshoe  fold  of  the 
Wamsutta  and  the  Pawtucket  area  of  these  rocks,  is  an  exposure  of  hard 
quartzose  conglomerate,  with  quartz  veins.  These  beds  evidently  underlie 
the  Wamsutta,  which  once  arched  over  them.  They  are  probably  con- 
tinuous with  the  Millers  River  outcrops   on  the  northwest,    though  that 


WAMSDTTA  GROUP.  141 

connection  can  not  now  be  traced.  A  few  bands  of  red  slate  occasion  their 
northern  upper  face 

jenks  Park  exposure  in  Pawtucket. — A  knob  of  finc  grittj  Conglomerate  occurs 
in  the  upper  part  of  Pawtucket  just  west  of  the  band  of  red  slates  belong- 
ing to  the  Wamsutta  series,  and  is,  like  them,  evidently  brought  to  the 
surface  by  a  fold. 

Other  exposures  of  the  conglomerate  occur  along  the  northern  margin, 
and  at  various  points  southward,  in  the  area  investigated  by  Dr.  Foerste. 

THE    WAMSUTTA    GROUP.' 

Devonian  or  Old  Red  Sandstone.  Edw.  Hitchcock:  Final  Report  on  the  Geology  of  Massachusetts, 
1841.  Catalogue  of  Rocks  in  Agricultural  Museum,  Sixth  Ann.  Rept.  Mass.  Board  of  Agric,  1859, 
Appendix,  p.  xxvii.     Mass.  House  Doc.  No.  39, 1853. 

Carboniferous.     Logan  and  Hall :  Geological  Atlas,  1865. 

Devonian  and  undetermined.     C.  H.  Hitchcock,  1871. 

Carboniferous.     Crosby  and  Barton :  Am.  Jour.  Sci.,  3d  series,  Vol.  XX,  1880,  pp.  416-420. 

Cambrian.     Shaler  and  Foerste,  1887.     (At  North  Attleboro.) 

Carboniferous.     J.  B.  Woodworth :  Am.  Jour.  Sci.,  3d  series,  Vol.  XL VIII,  1894.     (At  Canton  Junction.) 

The  name  Wamsutta  series  is  applied  in  this  report  to  the  red  strata  a 
part  of  which  were  mapped  as  Devonian  by  Edward  Hitchcock.  The  name 
is  used  in  a  geographical  and  lithological  rather  than  a  chronological  sense, 
for  it  is  evident  from  an  examination  of  the  field  that  these  red  rocks  are 
local  deposits  in  the  northern  part  of  the  basin  and  in  the  Norfolk  County 
Basin,  and  are  represented  by  ordinary  gray  and  carbonaceous  sediments 
farther  south.  An  exact  correlation  with  these  southern  beds  is  not  at 
present  possible.  Along  the  northern  margin  the  red  series  underlies  the 
Coal  Measures.     At  Pawtucket  it  is  interstratified  with  them. 

The  list  of  references  at  the  head  of  this  section  will  give  the  reader 
an  idea  of  the  various  opinions  held  regarding  the  age  of  these  beds.  The 
typical  area  in  North  Attleboro  was  definitely  shown  to  be  of  Carboniferous 
age  in  1887  by  Dr.  Foerste's  heretofore  unpublished  discovery  of  Carbonif- 
erous fossils  in  the  area  southwest  of  Reservoir  Pond  in  North  Attleboro. 

'  Wamsutta,  a  name  proposed,  but  not  actually  adopted,  for  North  Attleboro.  The  "  Wamsutta 
Mills"  are  situated  within  this  town.  Wamsutta  was  the  oldest  son  of  Massaaoit,  chief  sachem  of 
Pockanoket,  brother  and  predecessor  of  King  Philip.  He  was  named  Alexander  Pockanoket  by  the 
court  at  Plymouth,  June  10, 1660.  The  term  is  used  by  Dr.  Foerste  iu  his  thesis  on  this  field,  a  manu- 
script report  now  in  the  library  of  Harvard  University. 


142 


GEOLOGY  OF  THE  NARRAGANSETT  BASm. 


RED   ROOK    AREAS. 


There  are  eight  areas  in  the  northern,  part  of  the  basin  in  which  reddish 
rocks  have  a  surface  exposure,  and  in  these  they  are  brought  to  the  sm-face 
by  strong  folding.  1.  In  North  Attleboro  and  the  adjoining  towns  of  Wren- 
tham,  Massachusetts,  and  Cumberland,  Rhode  Island,  a  large  horseshoe- 
shaped  area  wrapping  about  a  knob  of  granitite  in  Hoppin  Hill  and  the 
North  Attleboro  Cambrian  outcrops.  2.  A  small  lens-shaped  area  extending 
northeastward  from  Central  Falls,  Rhode  Island,  into  Massachusetts.  3.  A 
still  smaller  area  south  of  the  last,  extending  northeastward  from  the  gorge 


/^rco  now  exposed  Area  probably  now  covered       Araa pmbobly  ero<iec^ au^oy 

.— >■     OirectiOfts  in  which  the  formation  c/ecrease^  in  thickness 
?      Passible  e'x/rosures 

riB.  11 Map  showing  distribution  of  red  sediments. 

of  the  Blackstone  in  PaAvtucket.  4.  A  characteristic  elongate  narrow  area 
extending  along  the  noithern  margin  of  the  main  basin  and  traceable  as  far 
as  the  North  River  in  the  town  of  Hanover.  This  area  is  probably  con- 
nected at  the  west  with  the  succeeding.  5.  The  largest  area  of  all,  extend- 
ing from  No.  1,  near  Sheldonville,  northward  and  eastward  to  Braintree, 
forming  the  greater  part  of  the  strata  in  the  Norfolk  County  Basin.  There 
are  exposures  in  (6)  Attleboro  and  (7)  Rehoboth,  and  one  in  (8)  Norton, 
which  may  belong  to  a  different  horizon.  I  shall  begin  the  account  of  these 
fields  with  the  area  along  the  northern  border  of  the  main  basin. 


WAMSUTTA  GROUP.  143 

THK  AREA  ALONG  THE  NORTHERN  BORDER. 

The  area  of  reddish  aud  chocolate-colored  strata  along  the  northern 
margin  of  the  basin,  from  near  Burnt  Swamp  Corner  eastward,  is  consid- 
ered first  for  the  reason  that  along  this  line  there  is  indubitable  evidence  of 
the  relative  positions  of  the  red  and  gray  rocks.  Throughout  the  extent  of 
this  northern  margin  the  red  conglomerates,  sandstones,  and  slates  occur  at 
or  near  the  base  of  the  Carboniferous  formation,  or  are  separated  from  it 
by  beds  of  arkose  and  gray  quartzose  conglomerates.  The  beds  can  be 
studied  along  the  border  in  Wrentham  about  three-quarters  of  a  mile  north 
of  the  Shepardville  reservoir,  in  two  small  hills  lying  west  of  the  stream 
which  comes  in  from  the  north.  Immediately  south  of  a  small  contact 
valley  between  the  granitite  and  the  Carboniferous  beds  of  the  border 
appear  red  sandstones  and  slates.  The  rock  is  pervaded  by  two  sets  of 
cleavage  planes  striking  about  in  the  line  of  the  border,  the  dip  of  one 
being  nearly  vertical  and  that  of  the  other  into  the  granitic  terrane  at  an 
angle  of  70°.  The  attitude  of  the  sedimentary  beds  is  not  very  plainly 
exhibited.  Limited  exposures  of  banding  indicate  a  strike  parallel  with 
the  border  and  a  southerly  dip  of  from  25°  to  30°.  The  outcrojjs  in  the 
western  knoll  show  red  sandstones  succeeded  by  greenish  sandstone,  which 
in  turn  is  succeeded  by  more  red  sandstone.  Near  this  locality  an  old  mill- 
stone made  out  of  a  reddish  conglomerate  with  small  quartz  pebbles  was 
seen  in  1894  built  into  the  fence.  The  greenish  sandstones  just  mentioned 
have  a  more  extensive  development  in  the  North  Attleboro  area  (p.  151). 

The  red  beds  are  well  exposed  on  the  southern  face  of  Foolish  Hill  in 
Foxboro.  They  here  dip  steeply  southward.  The  cleavage  dips  steeply 
northward.  Thin  bands  of  red  slate  may  be  seen  intercalated  between 
beds  of  whitish  arkose.  Red  conglomerates  with  quartzite  pebbles  also 
occur.  The  thickness  of  the  beds  is  difficult  to  obtain  with  accuracy,  but 
it  may  be  estimated  at  this  point  as  upward  of  1,000  feet. 

Red  beds  appear  to  the  east  near  the  contact,  at  some  points  conglomer- 
ates prevailing  over  sandstones.  The  thickness  evidently  diminishes  toward 
the  east,  but  exact  measurements  are  wanting.  The  red  color  of  the  basal 
rocks  also  declines  and  becomes  of  a  chocolate  hue.  The  strata  are  rarely 
deep  red  east  of  Brockton,  though  deep-red  slates  occur  northeast  of 
Abington.  In  the  eastern  part  of  the  field  red  conglomerates  are  no  longer 
recognized. 


144  GEOLOGY  OF  THE  NAERAGANSETT  BASIN. 

The  relative  paucity  of  granitic  pebbles  in  the  Wamsutta  conglomer- 
ates along  the  northern  border  is  evidently  due  to  the  previously  mentioned 
condition  of  the  gi'anitite  at  the  time  deposition  set  in.  Nowhere  is  there  a 
sharper  contrast  between  the  arkose  beds  and  the  red  shales  than  on  the 
southern  face  of  Foolish  Hill.  Bands  of  red  shale  here  alternate  with  the 
arkose  in  a  manner  to  show  that  the  small  particles  of  the  shale  brought 
with  them  their  coloring  matter  from  the  seat  of  denudation,  as  Russell  has 
argued  in  the  case  of  the  red  beds  of  the  Juratrias.^  The  importation  of  the 
oxide  of  iron  subsequent  to  deposition  would  have  colored  the  arkoses  and 
the  shales  alike. 

About  a  mile  southwest  of  Whiteville,  shown  on  the  Dedham  sheet, 
conglomerates  occur  dipping  gently  southward.  The  quartzite  pebbles  of 
this  rock  are  locally  brecciated,  and  their  surfaces  exhibit  a  kneaded  appear- 
ance on  the  matched  faces,  showing  clearly  that  brecciation  has  taken  place 
since  deposition.  The  waterworn  rounded  surface  of  the  original  pebble 
can  be  readily  traced.  These  dynamic  phenomena  indicate  that  the  strata 
along  this  northern  margin  have  never  been  under  the  pressure  which  has 
so  profoundly  acted  upon  the  elongated  conglomerate  pebbles  near  Newport, 
Rhode  Island. 

The  shallowness  of  the  waters — if  indeed  the  deposits  were  made  in  a 
permanent  water  basin — over  this  area  in  Wamsutta  time  is  shown  by  the 
current  marks  on  sandstone  layers  between  Whiteville  and  Easton,  and  by 
the  coarseness  of  the  sediments. 

The  structure  of  the  beds  is  everywhere  comparatively  simple,  their 
dip  being  southerly  beneath  the  carbonaceous  strata  which  begin  the  Rhode 
Island  Coal  Measures.  Their  continuity  is  frequently  interrupted  by  faults 
in  the  manner  explained  in  the  discussion  of  the  boundary  line  from  Burnt 
Swamp  Corner  eastward. 

Gray  sandstones  of  the  northern  border. — In  tlie  Small  hill  uear  tlio  border  uorthwest 
of  the  Shepardville  reservoir,  in  Wrentham,  there  are  exposures  of  a  brown- 
ish, sometimes  greenish,  fine-grained,  rather  massive  rock,  which  under  the 
microscope  is  seen  to  be  composed  of  grains  of  clastic  quartz  and  feldspar. 
This  rock  is  at  present  considered  as  a  member  of  the  Wamsutta  series,  and, 
on  account  of  its  more  extensive  development  a  few  miles  soiithward,  in 
North  Attleboro,  may  be  called  the  Attleboro  sandstone.     The  outcrops 

'  Subaerial  decay  of  rocks,  by  I.  C.  Russell :  Bull.  U.  S.  Geol.  Survey  No.  52, 1889,  p.  56. 


WAMSUTTA  GROUP. 


145 


along  tile  northern  border  are  of  much  importance  in  that  they  help  to 
define  the  stratigraphic  position  of  the  rock,  ft  is  here  interbedded  with 
the  red  conglomerates  and  shales. 

Traces  of  this  rock  are  seen  at  points  eastward  in  the  area  under  dis- 
cussion. Bowlders  of  a  similar  rock  bestrew  the  hillside  where  the  North 
River  passes  from  the  Carboniferous  area  into  the  region  occupied  by  the 
granitites.  Here  the  sandstone  is  well  bedded  and  alternates  with  bands  of 
pebbles  and  slate.  This  variety  of  sandstone  along  the  northern  border  is 
apparently  much  thinner  than  in  North  Attleboro.  The  probably  volcanic 
origin  of  this  rock,  in  the  form  of  ash,  is  referred  to  in  the  account  of  the 
occurrences  about  North  Attleboro. 


THE  NORTH  ATTLEBORO  AREA. 


The  most  characteristic  exposure  of  the  Wamsutta  group  occurs  as  a 
horseshoe-shaped  area,  open  on  the  north,  in  the  towns  of  Wrentham  and 


Fig.  12. — Geological  section  nortiiward  from  Kobinaoii  Hill, 


North  Attleboro,  Massachusetts,  and  Cumberland,  Rhode  Island.  The 
formation  is  a  series  of  conglomerates,  sandstones,  shales,  and  calcareous 
beds  with  associated  felsites,  felsite  breccias,  felsite  agglomerates,  and 
diabases.  A  characteristic  of  the  area  is  the  very  great  thickness  of 
conglomerates. 

Beginning  on  the  northeast,  the  formation  makes  its  appearance  abo^it  a 

mile  northeast  of  the  village  of  North  Attleboro,  in  Robinson  Hill  (see  fig.  12), 

an  eminence  which  overlooks  the  valley  excavated  in  the  softer  strata  of  the 

overlying  Coal  Measures  extending  westward  from  Mansfield.     The  section 

MON  xxxiii 10 


146  GEOLOGY  OF  THE  NAERAGANSETT  BASIN. 

from  this  point  to  the  northern  border  of  the  main  basin  seems  to  have  the 
form  of  an  overturned  syncline,  as  shown  in  tig'.  12. 

From  Robinson  Hill  the  red  conglomerates,  sandstones,  and  shales  can 
be  traced  southward,  with  strikes  conforming  in  direction  to  the  general 
distribution  of  the  formation,  to  Reservoir  Pond,  tlience  to  Rattlesnake  Hill 
and  skirting  the  northern  banks  of  Fourmile  Brook.  The  formation  thence 
trends  in  a  southwesterly  direction  to  South  Attleboro.  Good  exposures 
may  be  seen  in  Red  Rock  Hill.  Immediately  west  of  Washington  street 
and  south  of  Allen  road,  the  sandstones  and  conglomerates  may  be  seen 
turning  north-northwestward,  whence  they  continue  in  that  general  direc- 
tion as  a  broad  area  of  red  rocks  with  occasional  exposures  as  far  north  as 
the  vicinity  of  Burnt  Swamp  Corner.  A  well-marked  occurrence  of  these 
rocks  is  found  between  Abbots  Run  and  Millers  River. 

The  stratigraphy  of  the  area  immediately  west  of  the  Blake  Hill  fault 
block  in  Plainville,  and  thence  northward  to  the  Sheldonville  narrows,  is 
imperfectly  understood.  About  a  mile  north  of  the  southwest  corner  of 
the  block,  the  Wamsutta  beds  occur  in  a  well.  Between  this  locality  and 
the  Blake  Hill  schoolhouse,  1  mile  southeast  of  Burnt  Swamp  Corner,  gray 
Carboniferous  beds  appear  in  an  unknown  relation  to  the  red  beds  above 
referred  to.  From  the  schoolhouse  a  strip  of  red  conglomerates  extends 
southwestward  toward  the  main  belt  of  these  rocks,  which  here  skirt  the 
western  border.  The  varying  strikes  and  the  repetition  of  isolated  red  and 
gray  outcrops  northward  in  the  direction  of  Red  Brush  Hill  render  the 
structure  of  this  region  difficult  of  interpretation,  since  the  gray  beds  may 
belong  below  or  above  the  red  beds,  and  criteria  for  the  determination  of 
then-  position  are  there  absent.  The  boundary  line  drawn  upon  the 
accompanying  map  (PL  XVH)  between  the  red  and  gray  series  in  this 
region  is  therefore  ^^'holly  conjectural.  It  is  probable  that  the  rocks  are 
thrown  into  closed  folds. 

Conglomerates. — The  couglouierates  are  composed  mainly  of  waterworn 
pebbles  of  greenish  quartzite.  One  pebble  in  the  outcrops  in  the  valley  of 
Abbots  Run  contained  several  Obolus  shells,  which,  according  to  Walcott, 
are  upper  Cambrian.  Granitic  pebbles  are  common,  and  locally  there  is  a 
large  proportion  of  felsite.  Stretching  and  fracturing  of  pebbles  under  the 
pressure  of  strong  folding  is  evident  from  point  to  point  in  the  more  dis- 
turbed areas.     It  is  probable  that  conglomerates  occur  on  more  than  one 


'-'    £ 


WAMSDTTA  GROUP.  147 

horizon  in  this  field,  but  on  a(;count  of  the  intense  folding,  along  with  fault- 
ing, it  is  not  satisfactorily  determined  to  what  extent  the  conglomerates  are 
duplicated.  Some  of  the  felsitic  conglomerates  pass  into  agglomerates,  and 
these  into  felsite  breccias,  well  shown  in  the  valley  east  of  Oldtown. 

Sandstones. — The  saudstoues  of  the  area  under  discussion  are  of  variable 
texture,  becoming  coarse  and  feldspathic  and  thus  approaching  arkose 
on  one  hand  and  grading  into  quartzites  and  shales  by  the  separation  of 
the  quartz  and  decomposed  feldspar  on  the  other  hand.  The  reddish 
quartzitic  beds  are  well  exposed  on  Robinson  Hill  and  in  general  about  the 
village  of  North  Attleboro.  Their  detailed  representation  on  the  map 
accompanying  this  report  has  not  been  attempted.  In  the  bend  of  the 
sandstone  ridges  at  Red  Rock  Hill,  Mr.  H.  T.  Burr  found  rain  imprints  on 
the  sandstone. 

Shales. — The  shales,  or  often  slaty  argillaceous  sediments,  of  the  for- 
mation are  well  exposed  in  the  valley  between  Reservoir  Pond  and  Red 
Rock  Hill.  Other  exposures  occur  east  of  the  village  of  North  Attleboro. 
Reservoir  Pond  appears  to  lie  partly  in  a  depression  excavated  along  the 
line  of  strike  of  these  beds.  The  shales  are  frequently  interrupted  by 
knobs  and  sills  of  felsite  (see  fig.  14).  The  beds  contain  flattened  stems  of 
calamites,  as  at  Attleboro  Falls,  near  Reservoir  Pond,  and  east  of  Red  Rock 
Hill. 

THE  CENTRAL  FALLS  AREA. 

The  Central  Falls  area  is  not  well  exposed.  The  best  outcrops  are  near 
the  High  School  in  Central  Falls.  On  the  east,  near  the  old  post-road,  con- 
glomerates occur  with  slaty  beds  in  nearlj^  vertical  attitudes.  In  Pawtucket 
the  beds  are  mostly  red  shales  or  slates  at  the  same  high  angles.  The 
breadth  of  the  formation  decreases  rapidly  southward  along  the  strike.  At 
the  widest  part  it  is  as  much  as  1,000  feet.  Its  appearance  in  this  part  of 
the  field  is  evidently  owing  to  compressed  anticlines  and  synclines  in  the 
highly  inclined  Carboniferous  strata  at  the  head  of  Narragansett  Bay. 
The  structural  relations  of  this  area  to  that  in  North  Attleboro  ai-e  best 
explained  by  an  anticline  arching  over  the  conglomerates  west  of  South 
Attleboro.  This  view  also  supposes  that  some  of  the  Coal  Measures,  i.  e., 
the  Pawtucket  shales,  may  be  inferior  in  position  to  this  southern  extension 
of  the  red  beds. 


148 


GEOLOGY  OF  THE  NARRAGANSETT  BASIN. 


THE   PAWTUCKET  AREA. 


Another  small  area  south  of  the  last,  not  more  than  a  few  yards  in 
width,  is  exposed  in  the  gorge  of  the  Blackstone  River,  in  the  southern 
part  of  the  city  of  Pawtucket.  At  this  point  the  red  slates  are  associated 
with  green  slates,  recalling  a  similar  association  of  red  and  green  slaty 
beds  at  Pondville,  in  the  Norfolk  County  Basin.  Close  folding  appears 
also  to  be,  in  this  locality,  the  explanation  of  the  relations  which  these 
beds  bear  to  the  adjacent  carbonaceous  beds.  This  is  the  southernmost 
exposure  of  the  red  rocks  known  to  me  in  the  basin.  Southward  and  west- 
ward in  this  latitude  the  red  rocks  disappear.  At  only  one  point  on  the 
Little  Compton  shore  do  red  rocks  appear  at  the  surface  outside  of  the 
areas  named,  and  in  this  instance  they  are  limited  to  a  thin  layer  of  red 
hematite  in  the  coal-bearing'  section.  The  deposition  of  the  carbonaceous 
series  of  the  Coal  Measures  in  this  southern  field  preceded  the  incoming  of 


the  red  material  from  the  north,  and  continued  without  interruption  south 
of  Pawtucket. 

RED   BEDS   IN   ATTLEI50R0,    REHOliOTH,    AND   NORTON. 

These  occurrences  are  fully  considered  elsewhere  in  this  report.  Rea- 
sons will  be  advanced  in  the  following  chapters  for  regarding  at  least  the 
first  two  of  these  red  beds  as  local  deposits  formed  at  different  levels  in 
the  Coal  Measures.  The  last-named  area  contains  red  shales  with  calamites 
in  the  drift  a  few  rods  soutli  of  the  outcrop. 

NORFOLK  COONTV  BASIN  AREA. 

No  detailed  work  was  done  in  this  basin  during  the  present  survej^. 
As  a  result  of  a  reconnaissance,  fossils  were  found  at  Canton  Junction,  con- 
firming the  views  of  Crosby  and  Barton  as  to  the  Carboniferous  age  of  a 
part  of  the  strata.  The  rocks  closely  resemble  the  red  and  gray  beds  along 
the  northern  margin  of  the  main  basin.  Red  beds  largely  predominate  in 
all  the  exposures.  A  characteristic  basal  section  has  already  been  described 
at  Pondville.     The  strata  are  almost  everywhere  inclined  at  very  steep 


WAMSUTTA  GEOUr.  149 

angles.  While  the  section  at  Pondville  indicates  simple  downfolding  of 
the  margin,  the  form  of  the  basin  and  the  distribution  of  beds  along  the 
border,  particularly  on  the  north,  are  suggestive  of  downfaulting  of  the 
beds  in  most  parts  of  the  basin.  The  strata  are  usually  not  so  much  meta- 
morphosed as  those  south  of  Pawtucket  in  the  main  basin.  The  occurrence 
of  locally  metamorphosed  conglomerates  at  Morrills  Station  (see  fig.  6, 
p.  120),  on  the  Walpole  and  Wrentham  Railroad,  illustrates  the  effect  of 
great  pressure  in  producing  the  elongation  of  pebbles  and  in  inducing 
secondary  minerals.  In  this  instance  the  rock  has  become  very  markedly 
sericitic  and  disintegrates  rapidly. 

SOUTH  ATTLEBORO  LIMESTONE  BED. 

This  name  has  been  chosen  for  the  occuiTence  of  nodular  aggregations 
of  calcite  and  amorphous  carbonate  of  lime  which  are  associated  with  the 
red  shales  of  the  Wamsutta  or  red  rocks,  and  which  are  particularly  well 
displayed  in  South  Attleboro,  in  the  southern  base  of  the  hill  at  the  foot  oi 
which  the  town  is  situated. 

A  section  from  the  road  northward  up  the  hill  is  as  follows: 

Section  of  the  Wamsutta  formation  in  South  Attleboro,  Massachusetts. 

Feet.    In. 

Eed  shales,  concealed  southward 6  0 

Fine  conglomerate 2  0 

Red  shale 6 

Limestone  bed 6  0 

Shales,  red 10  0 

Conglomerate 5  0 

Shales,  red,  partly  covered 119  0 

Sandstone,  red 24  8 

Sliales,  red,  partly  concealed ,.  99  2 

(Felsite,  reddish  and  irregular  in  thickness,  exhibiting  flow  structure,  25  ft.) 

Shales,  red 28  4 

Red  conglomerate,  coarse  pebbles 60  0 

Shales,  red 60  0 

(Diabase,  amygdalar  cavities  on  northern  aspect,  15  ft.) 

Eed  shales,  concealed  northward,  measured 175  0 

The  limestone  occupies  irregular  kidney-shaped  cavities  in  the  red 
shale,  or  is  for  a  few  inches  of  its  thickness  in  the  form  of  rude  layers. 
Another  mode  of  occurrence  is  as  isolated  nodular  masses  half  an  inch  in 
diameter.     Tliese  nodules  are  frequently  elongated  in  the  direction  of  the 


150 


GEOLOGY  OF  THE  NARRAGANSETT  BASIK 


strike.  Some  of  the  larger  masses,  where  weathered,  show  minute  rounded 
apertures,  marking  closely  set  pits. 

Under  the  microscope,  in  thin  section,  a  specimen  of  the  amorphous 
limestone  fi-om  this  locality  appeared  as  an  aggregate  of  minute  grains, 
occasionally  exhibiting  large  individual  grains  with  distinct  cleavage. 

Stratigraphically,  the  limestone  is  at  this  point  relatively  low  down  in 
the  red  series  of  rocks.  The  material  can  be  traced  westward  and  north- 
ward, by  means  of  bowlders,  in  the  same  relative  position  on  the  east  side 
of  the  valley  of  Abbots  Run. 

Eastward  and  northward,  limestone  is  again  found  on  the  place  of  Mr. 
Todd,  near  the  old  Powder  House,  in  North  Attleboro ;  but  here  the  lime- 
stone is  a  mottled  marble,  which  has  been  used  for  making  quicklime.  The 
limestone  bed  here  occurs  in  a  thick  section  of  sandstones  and  shales  of  red 
color,  in  no  way  identifiable  with  the  section  in  South  Attleboro.  This 
occurrence  is  on  a  more  northern  line  of  outcrop  than  the  former,  and  if 
stratigraphically  connected  with  it,  is  to  be  explained  by  a  fold  such  as  is 
suggested  by  the  general  structure  of  this  area. 

The  irregularity  of  occurrence  of  the  limestone  in  the  different  sections 
where  it  is  exposed,  together  with  its  evident  secondary  origin,  has  led  to  no 
dependence  being  placed  upon  it  in  the  course  of  the  survey  as  a  plane  of 
reference  in  the  correlation  of  strata. 

Similar  shaly  limestone  reappears  in  the  Norfolk  County  Basin,  near 
Canton  Junction,  Massachusetts,  in  a  section  described  by  me.^  A  closely 
similar  rock  occurs  in  the  Cambrian  section  in  North  Attleboro,  where  the 
limestone  has  evidently  been  formed  from  the  remains  of  pteropods. 

These  limestones  were  described  by  Prof.  Edward  Hitchcock,  and  a  speci- 
men from  the  southwest  part  of  Attleboro  gave  him  the  following  analysis :  ^ 

Analysis  of  limestone  from  Attleboro,  Alassachitsetts. 


CaCO:, 

SiO-iandAljO,  . 


Quicklime 

Specific  gravity,  2.  71. 


94.60 
5.40 


100.  00 
52.98 


■  Am.  Jour.  Sci.,  3d  series,  Vol.  XLVIII,  1894,  p.  147. 

2  Final  Report  on  the  Geology  of  Massachusetts,  1841,  p.  80. 


WAMSUTTA  GROUP.  151 

The  late  Prof.  T.  Steny  Hunt  suggestecP  that  these  limestones  inter 
calatecT  with  red  slates  might  correspond  with  those  bands  of  limestone 
which  are  met  with  in  similar  red  slates  and  sandstones  at  the  base  of  the 
Carboniferous  formation  in  Canada  on  the  Bay  of  Chaleur  and  in  New 
Brunswick.  It  is  clear  that  the  deposits  lie  near  the  base  of  the  Car- 
boniferous in  Massachusetts,  but  the  evidence  is  as  yet  lacking  that  this 
section  corresponds,  in  the  sense  of  an  exact  correlation,  with  the  base  of 
the  Carboniferous  in  the  Canadian  provinces. 

Economically,  these  limestone  beds,  so  far  as  they  have  been  seen  in 
natural  exposures,  do  not,  in  the  presence  of  the  larger  and  purer  deposit 
in  the  neighboring  crystalline  region  of  Rhode  Island,  assume  a  commercial 
.importance.  As  a  local  source  of  supply  for  individual  uses,  they  will 
probably  from  time  to  time  afford  some  employment. 

ATTLEBORO   SANDSTONE. 

This  is  a  fine-grained  massive  sandstone,  varying  from  green  to  brown 
in  color,  the  latter  hue  being  due  evidently  to  oxidation. 

The  massive  structure  of  this  rock  and  the  angularity  of  its  particles  of 
quartz  and  feldspar  in  many  cases,  as  seen  under  the  microscope,  make  it 
likely  that  it  is  to  be  regarded  as  a  volcanic  ash  deposit,  discharged  from 
the  vents  which  gave  rise  to  the  felsite  flows  of  this  northwestern  corner  of 
the  basin. 

The  most  instructive  exposures  of  this  rock  are  in  the  town  of  North 
Attleboro.  One  may  be  seen  just  west  of  the  water  tower  in  the  north- 
eastern part  of  the  town.  A  more  extensive  outcrop  is  exposed  south  of 
Goat  Rock  and  north  of  the  Hoppin  Hill  granitic  area. 

Other  occurrences  of  this  rock  are  to  be  seen  embedded  with  the  red 
series  near  Robinson  Hill,  north  and  east  of  the  first-mentioned  locality, 
and  again  in  the  same  stratigraphic  relation  in  the  vicinity  of  Deantown, 
in  Attleboro  Township.  The  exposures  along  the  northern  margin  of  the 
basin,  in  the  Franklin  quadrangle,  show  the  position  of  the  deposit  to  be 
near  the  base  of  the  Carboniferous  formation.  The  quartz  grains  are  there 
much  coarser  than  in  North  Attleboro. 

The  stratigraphic  relations  of  the  sandstone,  where  seen,  indicate  that 

'  Am.  Jour.  Sci.,  3cl  series,  Vol.  XVIII,  1854,  p.  199. 


152  GEOLOGY  OF  THE  NARRAGANSETT  BASIN. 

it  is  a  member  of  the  Wamsutta  series.     Fossils  iiave  not  been  found  from 
which  to  determine  the  age  of  the  beds  independent!)'. 

The  texture  and  color  of  the  rock,  as  well  as  its  position  and  quantity, 
would  make  it  fit  for  building  stone  but  for  the  fact  that  it  is  quite  devoid 
of  those  sets  of  joints  or  bedding  planes  on  which  the  extraction  of  suitable 
blocks  depends. 

IGNBOOS   ASSOCIATES   OF   THE   WAMSUTTA    GROUP. 

One  of  the  striking  features  of  the  Narragansett  Basin  is  the  localiza- 
tion of  eruptive  rocks  in  the  area  of  the  red  strata  of  the  Wamsutta  group. 
Dikes  occur,  however,  elsewhere  in  this  region,  in  Lincoln,  near  Providence, 
and  at  the  mouth  of  Narragansett  Bay,  marginal  to  the  field. 

Diabase. — Au  interrupted  faulted  series  of  narrow,  partly  altered  diabase 
dikes  can  be  traced  from  North  Attleboro  southward  around  the  horseshoe 
fold  of  the  Wamsutta  group  to  Lanesville  and  thence  northward  toward 
Arnolds  Mills.  The  diabase  is  usually  erupted  through  red  conglomerate, 
sometimes  in  the  form  of  twin  dikes  with  a  large  sliver  or  wedge  of  the 
country  rock  between.  The  upper  surface  of  the  diabase  for  a  thickness  ot 
from  1  to  3  or  even  more  feet  is  commonly  vesicular;  sometimes  the  lower 
surface  is  amygdalar;  but  there  is  no  evidence  to  show  that  the  diabase 
flowed  out  as  a  contemporaneous  sheet. 

These  dikes  are  of  variable  widths  from  point  to  point  where  they 
appear,  attaining  thicknesses  of  from  20  to  50  feet.  They  frequently  rise  up 
as  low  black  knobs,  as  between  North  Attleboro  and  Attleboro  Falls,  or 
appear  as  low  bluffs,  as  on  the  east  bank  of  Abbots  Run  and  between 
Adamsdale  and  South  Attleboro.  For  the  most  part  they  crop  out  along 
the  outer  limits  of  the  circular  area  occupied  by  the  red  rocks. 

At  a  number  of  points  these  diabase  knobs  are  so  situated  as  to  be 
available  for  supphes  of  road  stone,  for  which  purpose  they  are  superior  to 
any  other  rock  in  this  district.  The  outcrops  at  Attleboro  Falls  are  within 
sight  of  the  railroad,  and  there  is  a  mass  adequate  for  local  uses  free  above 
ground  and  now  a  hindrance  to  house  building. 

The  ledge  on  the  Henry  Guild  place  in  Adamsdale  and  its  continuation 
northward  affords  another  source  of  suppl)^ — the  nearest  locality  of  trap  in 
workable  quantity  to  the  cities  of  Pawtucket '  and  Providence.  It  would 
require  a  carriage  of  a  mile  to  place  the  material  on  the  cars  of  the  New 
York,  New  Haven  and  Hartford  Railroad  at  Adamsdale  Station.     To  run  a 


WAMSUTTA  GROUP.  153 

spur  of  the  railroad  into  the  trap  locahty  would  necessitate  building-  a 
bridge  or  trestle  across  Abbots  Run.  From  a  point  half  a  mile  north  of 
the  station,  it  would  require  about  4,000  feet  of  track  to  reach  the  ledge. 

Quartz-porphyries,    felsites,  and  granophyres. Intimately      aSSOCiatcd      witll      tllC       red 

rocks  of  the  Wamsutta  group  is  a  series  of  acid  igneous  rocks  of  felsitic  and 
grauophyric  structure,  the  distribution  of  which  is  parallel  with  that  of  the 
diabase  dikes  just  described,  and,  like  the  former,  these  rocks  occur  in  knobs, 
whether  true  bosses  or  faulted  and  disjointed  dike-like  masses  being  not 
easily  determined.  In  general  they  are  limited  to  the  horseshoe  fold,  and 
do    not    accompany  the   Wamsutta   group    eastward    along   the    northern 


Fig.  14. — Section  tlirough  felsite  knob  in  Attleboro,  Massacliusetts.    (See  table  below.) 

margin  of  the  basin  nor  in  the  Norfolk  County  Basin  beyond  the  narrows 
in  Wrentham.     The  felsites  are  usually  of  a  reddish  color. 

A  cross  section  (fig.  14)  of  one  of  these  knobs  south  of  Reservoir  Pond 
illustrates  the  general  character  of  the  association  with  the  Wamsutta  group. 

The  succession,  beginning  on  the  east,  is : 

Section  south  of  Reservoir  Pond. 

reet. 

Sandstone  (red,  pebbly)  and  shale  (red) 40 

Diabase 40 

Felsite 10 

Conglomerate,  red 8 

Felsite,  in  large  knob 50 

(Western  contact  not  seen.) 


154 


GEOLOGY  OF  THE  NAEEAGANSETT  BASIN. 


The  felsites  frequently  occur  higher  up  stratigraphically  than  the 
intruded  diabases.  The  following  scheme  of  arrangement  of  rocks  at  three 
localities  will  represent  this  fact: 

Stratigraphic  relations  of  felsite  and  diaiase  at  three  localities. 


(IT,  Z.24.) 

(VII,  D.  20.) 

(VII,  B.  7.) 

Red  sliale. 

9 

? 
9 

? 
9 

i 

Felsite. 

Felsite. 

Felsite. 

Conglomerate. 

f 

Conglomerate. 

Diabase. 

Diabase. 

Diabase. 

Shale. 

Shale. 

Shale. 

Conglomerate. 

Conglomerate. 

? 

? 

? 

Diabase. 

f 

Conglomerate. 

? 

? 

? 

Shale. 

? 

? 

Conglomerate. 

This  matching  of  short  sections  within  2  or  3  miles  of  each  other,  the 
first  two  being  within  half  a  mile,  illustrates  something  of  the  constancy  of 
occurrence  of  these  igneous  rocks.  Regarded  as  a  map,  the  bottom  of  the 
table  is  east,  the  top  west.  The  interrogation  marks  indicate  the  places  of 
concealed  strata.  The  persistent  failure  of  the  western  contact  of  the  felsite 
is  a  noticeable  feature,  due  to  the  erosion  and  concealment  of  softer  material. 

The  large  felsite  mass  between  the  village  of  South  Attleboro  and  Red 
Rock  Hill  causes  the  strata  to  separate  in  the  manner  of  a  tilted  laccolith, 
but  contacts  have  not  been  observed  which  verify  the  view  that  it  is  one. 
Flow  structure,  often  attended  with  crumpling  of  the  layers,  is  manifest  in 
many  outcrops  of  this  rock. 

Beneath  the  massive  flow  of  the  felsite  is  a  zone  of  the  same  rock,  form- 
ing the  matrix  of  an  agglomerate,  composed  of  rounded  pebbles  of  felsite 
and  quartz-porphyry,  together  with  quartzite  and  occasional  pieces  of  horn- 
blendic  granitite.  This  lower  bed  is  several  feet  thick.  In  South  Attleboro 
there  is  exposed  a  bed  having  a  thickness  of  more  than  10  feet.  The  water- 
worn  pebbles  are  evidently  fragments  caught  up  in  a  movement  or  flow  of 
the  felsite  over  earlier  conglomerates.  The  groundmass  of  this  agglomerate 
is  porphyritic,  with  a  plagioclase  feldspar  in  every  respect  like  that  of  the 
overlying  mass. 


WAMSUTTA  GROUP.  155 

The  eruptions  of  felsite  in  this  field  appear  to  have  taken  place  some- 
tivne  after  the  deposition  of  the  first  sediments  of  the  Carboniferous  section 
and  before  the  laying  down  of  the  Coal  Measures  along  the  northern 
border.  These  members  of  the  quartz-porpyhry  family  of  igneous  rocks  are 
but  outliers  of  more  extensive  eruptions  of  a  closely  related  magma  which 
is  extensively  intruded  into  the  rocks  of  the  Boston  Basin  or  is  found  there 
as  ancient  flows.  In  that  area  the  age  of  the  eruptions  is  not  precisely 
known.  If  the  evidence  from  the  area  of  the  Wamsutta  group  in  North 
Attleboro  and  the  case  in  Plympton  can  be  relied  upon  as  evidence,  it 
would  point  to  the  Carboniferous  age  of  these  eruptives  in  the  vicinity 
of  Boston,  and  probably  to  an  epoch  later  than  the  lower  Carboniferous 
proper. 

DIAMOND   HII.L   QUARTZ   MASS. 

Lying  on  the  western  border  of  the  Wainsutta  group,  but  apparently 
developed  in  these  Carboniferous  sediments  and  in  the  felsites,  is  the  large 
mass  of  vein  quartz  known  as  Diamond  Hill.  The  quartz  occurs  prevail- 
ingly in  the  vein  form,  with  layer  upon  layer  of  divergent  pyramidal-faced 
crystals.  Locally  the  quartz  is  chalcedonic  and  wliite,  earthy,  opaline,  the 
whole  being  evidently  the  product  of  hot  springs  following  the  decadence 
of  igneous  action  in  this  ai-ea. 

Quartz  veins  having  the  same  structure  and  habit  penetrate  the  red 
sandstones  of  the  Wamsutta  group  along  the  northern  boundary  in  Wren- 
tham.  This  habit  of  crystallization  has  not  been  detected  elsewhere  in  the 
basin,  although  extensive  quartz  masses  occur  at  other  points,  as  at  Mount 
Hope,  and  in  less  abundance  southward  in  the  bay  region.  It  is  highly 
probable  that  the  deposition  of  this  quartz  took  place  during  Wamsutta 
time. 

WAMSUTTA  VOLCANOES. 

The  peculiar  features  of  the  Wamsutta  series — the  rapid  thickening  of 
the  sandstones  and  conglomerates  toward  the  northwest  corner  of  the  present 
area,  the  felsites  with  definite  flow  structure,  the  gray  ash  beds  or  Attleboro 
sandstone,  the  agglomerates  of  felsitic  material,  and  the  associated  conglomer- 
ates composed  in  large  part  of  felsite  pebbles — all  point  to  a  volcano  or  volca- 
noes existing  in  this  field  in  Carboniferous  time.  The  known  petrographic 
connection  between  the  flow  structure  of  felsites  in  extrusive  masses  and  the 
coarser  structure  of  typical  granite-porphyries  in  stocks  and  dikes  brings 


156 


GEOLOGY  OF  THE  NAEEAGANSETT  BASIN. 


the  plienomena  of  the  Wamsutta  sei'ies  in  North  Atlleboro  and  the  under- 
lying terrane  of  schists  with  intrusive  granite-poi'phyries  in  Cumberland  into 
an  interpretable  relation.  On  the  one  hand,  we  have  the  effusive  products 
of  volcanic  action;  on  the  other  hand,  the  underground  conduits-  and  rents 
filled  with  their  equivalent  portions  of  the  magma. 

The  same  story  is  fairly  derived  from  the  Blue  Hill  region  on  the 
north  side  of  the  Norfolk  County  Basin.  The  beginning  of  sedimentation 
in  this  part  of  the  Carboniferous  land  area  aptpears  clearly  to  have  been 
accompanied  by  extensive  acid  eruptions.  It  is  probable,  as  above  noted, 
that  the  large  felsite  area  about  Boston  was  formed  also  in  Wamsutta  time. 
How  much  later  the  action  continued  can  not  be  readily  determined.  The 
intrusion  of  pegmatitic  granites  in  the  southern  arm  of  the  Narragansett 
Basin,  in  the  Aacinity  of  Watsons  Pier,  together  with  the  marked  local  meta- 
morphism  of  all  the  Carboniferous  strata  in  that  portion  of  the  area,  shows 
that  volcanic  action  held  on  there  later  than  in  the  northern  fields,  if  it  did 


M/7/ers /f/Ver         Abbots  Run 


Hoppi'n  ///// 


Fig.  15.— Geological 


not  altogether  take  place  later  than  the  deposition  of  the  Carboniferous 
strata  in  this  part  of  the  continent. 


I'OLDING   OF   THE    WAiMSUTTA   GROUP. 


The  folds  of  the  strata  of  the  red  Wamsutta  series  in  North  Attleboro 
are  the  most  complicated  that  have  been  found  in  the  Narragansett  Basin. 
The  large  horseshoe-shaped  area  of  red  rocks  above  described  wraps 
around  the  older  granitite  and  Cambrian  rock  of  Hoppin  Hill,  so  that 
the  general  structure  is  anticlinal;  but  the  dips  of  the  beds  are  now 
in  many  places  inward  toward  the  center,  giving  rise  to  an  apparent 
synclinal  structure.  On  the  east,  from  the  village  of  North  Attleboro 
southward  to  South  Attleboro,  the  dips  of  the  red  beds  are  mainh^  inward 
toward  the  Hoppin  Hill  area,  until  at  the  latter  place  they  become  very 


WAMSUTTA  GEOUP. 


157 


low,  as  ill  the  nose  of  a  broad  shallow  syncline  (see  fig.  15).  On  the 
western  arm  of  the  area  the  dips  vary  from  east  to  west.  Such  marked 
inversion  of  strata  warrants  the  explanation  that  the  beds  have  been  com- 
pressed into  the  fan  structure  by  the  marginal  collapse  of  a  more  or  less 
quaquaversal  anticline  which  formed  over  the  Hoppin  Hill  inlier.  It  is 
owing  to  this  extreme  folding,  together  with  the  imperfection  of  the  expo- 
sures by  reason  of  glacial  di-ift,  that  the  region  is  so  difficult  of  interpreta- 
tion. Northward,  near  Arnolds  Mill,  the  apparent  structure  is  indicated  in 
the  section,  fig.  16. 

In  the  southern  areas  of  red  rocks  in  Pawtucket  there  is  the  most  sat- 
isfactory reason  for  believing  that  the  broad  exposures  of  alternating  red 
and  gray  rocks  are  due  to  close  folding.  This  district,  indeed,  furnishes  a 
clue  to   the   structure  of   the  nearly  vertical   beds   southward   along  the 


w.s.w. 


Fig.  10.— Geolugical  section  in  the  Arnolds  ilill: 


western  margin  of  the  Narragansett  Basin,  in  the  Cranston  beds,  and  in  the 
equivalent  Kingstown  series,  described  by  Dr.  Foerste  in  another  section  of 
this  monograph. 

This  same  field,  showing  the  red  and  gray  Carboniferous  strata  folded 
into  isoclinal  relations,  affords  strong  evidence  for  believing  that  the  Wam- 
sutta  series,  in  the  main  basin  at  least,  was  not  folded  until  the  deposition 
of  the  Coal  Measures,  and  that  the  entire  thick  section  of  sediments  in  the 
basin  underwent  phcation  after  the  period  of  deposition.  All  the  facts  from 
various  points  in  the  field  support  the  view  that  there  was  but  one  period 
of  elevation,  and  not  two,  as  was  formerly  thought  by  Edward  Hitchcock. 
There  are  a  few  disturbances  along  the  northern  margin  in  the  Wamsutta 
area,  which  have  been  thought  to  indicate  an  upturning  of  the  red  series 
before  the  deposition  of  the  Coal  Measures  in  that  section,  but  to  my  mind 
the  evidence  is  not  clearly  demonstrative  of  this  view. 


158  GEOLOGY  OF  THE  NARRAGANSETT  BASIN. 

Several  small  faults  exist  in  the  North  Attleboro  area  between  Robin- 
son Hill  and  South  Attleboro.  These  dislocations  are  indicated  by  the 
offset  of  diabase  dikes  along  their  line  of  strike,  by  the  occurrence  of  beds 
in  blocks,  and  also  bv  the  exposures  in  which  the  dislocation  may  be 
traced.  In  front  of  the  house  of  Mr.  H.  Rhodes,  about  1^  miles  northeast 
of  South  Attleboro,  reddish  sandstones  are  brought  against  the  red  slates, 
but  this  relation  is  probably  due  to  local  unconformity  rather  than  to  a 
fault. 

FLOHA    OF    THE    WAMSUTTA    (iROHP. 

So  far  as  the  observations  of  the  present  survey  g'o,  the  sole  fossils 
found  in  the  red  shales  and  sandstones  of  this  series  by  Dr.  Foerste  and 
myself  are  a  species  of  calamites  and  a  cordaites.  As  a  whole,  the  strata 
are  prevailingly  barren,  a  characteristic  of  red  rocks  everywhere.  Enough 
of  the  flora  is  known,  however,  taken  together  with  the  stratigraphy,  to 
warrant  placing  the  beds  in  the  Carboniferous  section  of  the  Narragansett 
Basin.  This  fully  confirms  the  views  of  Crosby  and  Barton  expressed  in 
1880. 

The  geographical  conditions  under  which  the  beds  Avere  laid  down 
seem  to  have  been  incompatible  with  the  accumulation  of  j^lant  remains  in 
the  area  of  sedimentation,  rather  than  that  there  is  any  difficulty  in  preserv- 
ing fossils  of  this  kind  in  red  beds.  In  places  abundant  traces  of  calamites 
occur  in  the  form  of  good  impressions  without  a  trace  of  Carbonaceous 
matter.  In  other  localities  the  impressions  of  single  stems  are  black  with 
carbon,  and  had  enough  of  these  fragments  been  accumulated  in  one  plane 
a  black  shale  layer,  if  not  a  deposit  of  coal,  must  undoubtedly  have  resulted. 

There  are  reasons  for  believing  that  southward  beyond  the  limits  of 
the  red  beds  plant  remains  were  accumulating  at  this  early  stage  in  the 
Carboniferous  of  the  Rhode  Island  area.  The  general  absence  of  fossils 
in  this  series  appears  to  have  been  due  to  a  control  exercised  by  the 
peculiar  processes  concerned  in  the  deposition  of  the  series  itself  The  pres- 
ence of  quartz-porphyry  pebbles  along  Avith  masses  of  this  rock  and  the 
related  felsite,  which  appear  to  have  come  into  their  present  relation  to  the 
strata  before  the  deposition  of  the  Coal  Measures  in  this  part  of  the  field, 
suggests  that  volcanic  action  may  have  affected  the  formation  of  sediments 
in  a  way  to  be  locally  unfavorable  to  the  growth  and  preservation  of  plants. 


THE  OARBONIFEEOUS  STRATA.  159 


COAL  MEASURES. 


The  Rhode  Island  Coal  Measures,  if  we  use  this  term  to  comprise  all 
the  horizous  on  which  coal  has  been  reported,  include  at  one  point  or 
another  in  the  basin  all  the  strata  from  near  the  base  to  the  great  con- 
glomerate bed  which  occurs  at  the  bottom  of  the  Dighton  group.  The 
estimated  thickness  of  this  section  is  about  10,000  feet. 

There  is  reason  to  believe  that  the  lowest  members  of  this  great  thick- 
ness of  sediments  are,  from  Pawtucket  southward,  the  time  equivalents  of 
the  Wamsutta  group.  The  relations  of  the  Wamsutta  series  of  red  and 
green  slates  to  the  coal  shales  may  be  seen  to  advantage  in  the  gorge  of 
the  Blackstone  River  at  Pawtucket. 

The  very  considerable  thickness  of  the  beds  between  the  basal  arkoses 
and  the  conglomerates  and  the  overlying  Dighton  group  of  conglomerates 
has  rendered  it  possible  to  make  certain  divisions  in  this  great  middle  section 
which  have  a  geographical  value  and  indicate  at  the  same  time  lithological 
peculiarities.  On  these  grounds  four  groups  have  been  denominated,  it  not 
being  satisfactorily  determined  whether  the  strata  of  the  lower  two  beds 
are  exactly  equivalent  or  not. 

The  supposed  relations  of  these  to  the  beds  recognized  b}^  Dr.  Foerste 
farther  south  are  indicated  in  the  table  on  page  134. 

In  the  following  notes  concerning  the  northern  area  local  names  will 
be  employed,  with  such  chronological  limitations  as  present  knowledge  of 
the  field  will  permit 

CRANSTON  BEDS:  KINGSTOWN  SERIES  OF  DR.  FOERSTE. 

PKOVIDENCH   AREA. 

It  is  the  general  opinion  of  those  who  have  examined  the  rocks  west 
of  Narragansett  Bay  in  the  ^dcinity  of  ProAddence  that  the  strata  of  the 
Coal  Measures  are  here  nearer  the  base  of  the  series  than  those  which  lie 
immediately  on  the  east  of  Providence.  This  supposition  is  borne  out  by 
the  structure  of  the  sections  which  can  be  drawn  for  this  region. 

The  strata  of  this  area  from  Pawtucket  southward,  to  the  limits  of  the 
Providence  sheet,  exhibit  generally  very  steep  dips  prevailingly  eastward. 
The  strikes  are  generally  east  of  north,  being  more  persistent  in  the  sand- 


160 


(lEOLOGY  OP'  THE  NARRAGANSETT  BASIN. 


stone  beds  than  in  the  shales,  the  latter  being  very  much  crumpled  and 
often  striking  east  and  west. 

The  metamorphism  of  this  belt  allies  it  petrographically  with  the  area 
southward  in  the  lower  part  of  Narragansett  Bay.  The  sandy  and  pebbly 
beds,  however,  exhibit  less  dynamic  metamorphism,  but  the  shales  above 
exhibit  in  a  marked  degree  the  development  of  new  minerals  which  has 
resulted  from  this  change. 

There  are  three  well-marked  north-south  troughs  about  Providence 
in  which  the  softer  argillaceous  beds  occur,  separated  by  more  resistant 
arenaceous  strata  standing  out  as  ridges.     Beginning  on  the  west,  and  next 


\  See /f  on  A  River 


East  Prov/dence 

I  Ten  Mile  River 


Fig.  17. — Hypothetical  geological  section  east  aud  west  througli  Providence,  Khode  Island,  showing  supposed  relations  of 
Cranston  and  Tenmile  River  beds. 


the  escarpment  which  marks  the  crystalline  and  igneous  border,  there  is 
the  depression  between  it  and  Sockanosset,  Rocky,  Sky  High,  Bradley, 
and  Windmill  hills.  The  structure  and  character  of  the  strata  occupying 
this  depression  can  be  inferred  only  from  isolated  observations,  mainly  in 
the  "dugway"  in  the  southwestern  part  of  Cranston,  where  the  basal  beds 
of  the  Carboniferous  cling  to  the  escarpment  in  a  recess.  The  next  trough 
on  the  east,  which  opens  out  into  the  bay  south  of  Providence,  is  very 
thoroughly  filled  in  with  glacial  sand  plains.  The  occurrence  of  conglom- 
erates toward  the  south  and  the  evidence  from  borings  in  the  vicinity  of 
Providence  are  the  sole  indications  of  the  stratigraphy. 


RHODE  ISLAND  COAL  MEASURES.  161 

The  coal  from  Cranston  afforded  F.  A.  Gooch  the  following  analysis:^ 

Analysis  of  coal  from  Cranston,  Rhode  Island. 


Per  cent. 

Water 

0.24 
4.49 
82.20 
13.07 

Volatile  matter 

Fixed  carbon 

Ash 

Total 

100.  00 
0.34 

Specific  gravity,  2.209  at  150-\ 

These  trong-hs  appear  to  be  mainly  underlain  by  coal-bearing-  shales. 
The  Sockanosset  mine  in  Cranston  comes  in  this  section.  In  the  valley 
north  of  Providence  the  shales  crop  out  in  a  cut  in  the  Old  Colony 
Railroad. 

A  well  sunk  in  Butler  street,  corner  of  Bassett  street,  in  1895,  penetrated 
the  Coal  Measures.  Samples  of  the  materials  brought  up  from  certain 
depths  were  furnished  the  Survey,  through  Mr.  N.  H.  Darton,  by  Mr.  C.  A. 
Ray,  of  East  Providence,  Rhode  Island.  The  following  table  sets  forth  the 
data  obtained  from  this  well. 

Record  of  well  sunk  in  Providence,  Rhode  Island,  in  1895. 

Depth  in 
feet. 

Schist,  soft,  black,  graphitic;  with  water  turning  to  graphitic  mud,  somewhat 

too  gritty  for  lubricating  j)urposes 126 

Schist,  micaceous,  carbonaceous,  carrying  large  cubical  iron  pyrites 176 

Schist,  carbonaceous 309 

Schist,  graphitic 341 

Grit,  or  metamorphic  sandstone 352.  5 

Schist,  graphitic,  with  fragments  of  vein  quartz _ 419 

Goal,  anthracitic;  very  light,  with  small   cubic  fracture  and  some  irregular 

patches  of  dull  black  carbon 460 

Coal,  cut  by  veins  of  quartz,  subflbrous  near  walls 475 

Coal,  with  small  cubical  fracture  and  more  of  the  dull  lusterless  carbon,  about.  477 

Schist,  heavy,  black,  graphitic,  pyritiferous,  about 477 

Schist,  line  micaceous,  pyritiferous  in  layers ; 492 

I  Report  of  work  done  in  the  Washington  laboratory  during  the  fiscal  year  1883-84 :  Bull.  U.  S. 
Geol.  Survey  No.  9,  1884,  p.  18. 
MON    XXXIII 11 


162 


GEOLOGY  OF  THE  NARRAGAJSfSETT  BASIN. 


Pawtucket  shale 


-Still  farther  northward  in  Pawtucket  the  shales  are  well 
exposed  in  the  banks  of  the  Blackstone  River  on  Division  street,  and  at 
Valley  Falls  they  are  exploited  in  a  graphite  mine. 

The  best  natural  exposure  is  along  the  eastward  bend  of  the  Black- 
stone  River  between  Central  Falls  and  Valley  Falls,  where,  on  the  south 
bank  of  the  river,  a  section  of  bluish  and  black  carbonaceous  shales,  Avith 
fossils,  is  thrown  into  a  broken  fold  with  minor  contortions  (see  fig.  18). 
The  strike  here  is  approximately  east  and  west,  and  the  dips  are  steep, 
mainly  80°  N.  The  beds  evidently  overlie  the  grits  and  red  series  half  a 
mile  south.  The  slate  layers  contain  distorted  and  disjointed  fragments  of 
plants.     Further  evidence  of   the   movement  which   the   rock   has  under- 


m»i  mm 


Fig.  18.— Folded  and  faulted  Carboniferous  shales  on  the  Blackstone  Eiver  at  Pawtucket,  Khode  Island.      (Looking-  east.)- 

gone  is  shown  in  minute  joints,  in  antiparallel  sets,  accompanying  small 
puckerings  of  the  slate.  Along  each  joint  plane  there  has  been  a  minute 
fault  movement  of  the  normal  kind. 

The  thickness  of  the  beds  included  under  the  term  Pawtucket  shales, 
if  we  place  here  all  the  soft  beds  in  the  troughs  so  far  described,  can  not  be 
safely  stated.  If  the  structure  about  Providence  is  due  to  the  duplication 
of  beds  by  overturned  folds,  as  indicated  in  the  theoretical  section  (fig.  17, 
p.  160),  and  since  there  are  at  least  3,500  feet  of  beds  between  the  sandstones 
of  the  Avestern  or  Sockanosset  ridge  and  the  base  or  western  boundary,  the 
apparently  great  thickness  of  beds  in  the  other  valleys  may  be  readil}- 


EHODE  ISLAND  COAL  MEASURES.  163 

explained.     How  much  of  this  section  is  to  be  allotted  to  the  shales  alone 
is  not  known. 

sockanosset  sandstones. — Tlic  I'idgBS  in  this  area,  including  the  ridge  in  the 
East  Side  area,  are  evidently  due  to  the  jDresence  of  sandstones  and  con- 
glomeratic beds.  They  are  well  exposed  on  Sockanosset  ridge  east  and 
west  of  the  reservoir.  They  are  members  of  the  Kingstown  series  of  Dr. 
Foerste.  The  shales  are  carried  well  up  on  the  eastern  flanks  of  these  hills. 
PI.  V  represents  a  side  view  of  Rocky  Hill,  showing  the  glaciated  northern 
slope. 

BAST   SIDE   AREA  IN   PKOVIDENCE. 

Knowledge  of  the  stratigraphy  of  this  area  is  limited  to  a  few  out- 
crops and  to  occasional  borings,  the  latter  of  which  have  been  recorded  by 
the  Providence  Franklin  Society.^ 

The  rocks  consist  of  sandstones,  shales,  and  pebbly  beds,  exhibiting  the 
aspects  of  metamorphism  commonly  found  farther  south  at  Sockanosset  and 
in  the  lower  bay  region.     The  schists  are  frequently  highly  carbonaceous. 

The  rock  reported  to  have  been  taken  from  the  ledge  on  which  Roger 
Williams  landed  is  a  black  metamorphic  shale,  or  ilmenite-schist,  soft  and 
readily  falling  to  pieces  under  abrasion.  This  rock  evidently  gives  rise  to 
the  depression  in  which  the  Providence  and  Seekonk  rivers  run. 

The  attitude  of  the  strata  in  this  area  is  exhibited  in  the  outcrop 
opposite  No.  75  East  George  street,  near  Glano  street.  There  are  here 
about  38  feet  of  slates  with  arenaceous  and  pebbly  beds,  all  showing  signs 
of  crumpling  under  great  pressure  and  standing  at  angles  of  dip  as  high  as 
80°.  The  beds  strike  N.  25°  E.  magnetic  (N.  14°  E.),  dipping  in  one  place 
E.,  in  another  W.  The  fine  conglomerates  contain  quartz  and  quartzite 
pebbles.  There  is  a  pronounced  cleavage,  for  the  most  part  striking  N.  65° 
W.  magnetic  (N.  76°  W.),  and  dipping  about  60°  N.  This  secondary 
structure  seems-  generally  to  have  been  taken  by  the  inexpert  for  strati- 
fication. Similar  exposures  exist  on  the  hill  to  the  west.  Rock  is  also 
reported  to  have  been  struck  in  borings  at  a  few  feet  from  the  surface  and 
in  making  excavations  for  the  reservoir.  Coal  is  said  to  have  been  met 
with  on  Benefit  street  south  of  Church  and  Stair  streets. 

On  the  land  of  the  Swan  Point  Cemetery,  between  Swan  Point  road 
and  Blackstone  boulevard,  is  a  small  outcrop  of  massive  grayish  sandstone, 

i  Geolosy  of  Ehodo  Island,  1887,  Addenda,  pp.  129-130, 1888. 


164  GEOLOGY  OF  THE  NARKAGANSETT  BASHST. 

sucli  as  is  characteristic  of  the  Coal  Measures  on  the  east  side  of  Providence 
River.  The  rock  exhibits  a  fissile  structure,  striking  N.  25°  E.  magnetic 
(N.  14°  E.)  and  dipping  60°  E.  These  figures  give  also,  I  believe,  the 
approximate  attitude  of  the  stratum 

TENMILE   RIVER  BEDS. 

The  Coal  Measures  east  of  the  Providence  and  Seekonk  rivers  as  far 
as  the  eastern  bank  of  the  Tenmile  River  afiFord  characteristic  exposures  of 
slightly  altered  sandstone,  pebbly  beds,  and  shales.  Coal  has  been  found  in 
the  bed  of  Tenmile  River.  These  strata  may  for  reference  be  denoted  as 
the  Tenmile  River  beds.  The  essential  features  of  this  horizon  are  set  forth 
in  the  following  description  of  localities.  If  the  beds  on  the  west  side  of 
the  Seekonk  and  Providence  rivers  are,  as  the  local  structures  indicate,  in  an 
anticlinal  relation  with  those  on  the  east  side  of  those  streams,  the  meta- 
morphosed shales  and  sandstone  of  the  Cranston  series  are  the  equiva- 
lent of  the  Tenmile  River  beds.  For  the  present  it  seems  best  to  consider 
the  beds  as  two  geographical  groups.  The  presence  of  the  Odontopteris 
flora  and  the  insect  fauna  in  the  Tenmile  River  beds  allies  them,  it  should 
be  noted,  with  the  metamorphosed  strata  at  Pawtucket  and  Sockanosset, 
and  favors  the  idea  that  the  two  series  are  essentially  at  the  same  horizon, 
though  it  is  probable  that  the  Tenmile  beds  do  not,  as  does  the  Cranston 
series,  run  downward  to  the  base  of  the  Coal  Measures.    (See  fig.  17,  p.  160.) 

LEBANON  MILLS  EXPOSURE. 

A  low  outcrop  in  which  there  is  a  small  quarry  occurs  on  the  west  bank 
of  the  Tenmile  River  at  Lebanon  Mills.  The  beds  are  conglomerates, 
sandstones,  and  slaty  shales,  striking  N.  48°  E.  and  dipping  70°  S.  One  of 
the  slaty  layers  contains  worm  burrows  and  plant  stems  (Sigillaria,  Cala- 
mites),  and  the  beds  have  here  and  there  a  reddish  hue.  The  beds  clearly 
underlie  those  on  the  east  bank  of  the  river. 

EAST   PROVIDENCE   AREA. 

Very  good  exposures  occur  in  the  southern  part  of  the  town  of  East 
Providence,  Rhode  Island,  in  quarries  near  Leonards  Corners,  and  particu- 
larly along  the  shore  of  Narragansett  Bay  from  Watchemocket  Cove  south- 
ward to  near  Sabins  Point.  The  strata  in  this  area  are  in  marked  contrast 
to  the  exposures  on  the  west  side  of  the  Seekonk  and  Providence  rivers. 


RHODE  ISLAND  COAL  MEASURES. 


165 


G/ac/a/  drift 


as  regards  both  attitude  aud  alteration.  They  not  only  he  in  less  disturbed 
positions,  but  they  preserve  to  a  much  greater  degree  their  original  clastic 
texture,  and  fossils  are  of  frequent  occurrence  in  them.  An  account  of  the^ 
more  typical  exposures  as  they  now  exist  follows: 

Leonards  Corner  quarries. — In  the  soutlieastem  triangle  formed  by  the  roads, 
at  an  elevation  of  about  100  feet  above  the  sea,  is  an  exposure  of  pebbly 
sandstone  on  the  site  of  ■-  a  rock  crusher.  The  strike  here  is  about  east-west 
and  the  dip  very  gently  to  the  south.  An  unidentifiable  fossil  tree,  over  9 
feet  in  length  and  from  6  to  8  inches  in  diameter,  lies  prostrate  in  the  bed- 
ding, with  its  major  axis  east-west. 

A  half  mile  east  of  the  outcrop  just  described,  about  25  feet  of  the 
coarse  pebbly  sandstone  of  the  Carboniferous  are  exposed  in  Mr.  John 
McCormick's  quarry.  The  beds  are  massive,  essentially  horizontal,  with 
traces  of  coaly  shales  and  coal,  the  last 
mostly  marking  the  sites  of  single  plants. 
The  following  plants  were  found: 

Calamites  suckovii,  in  large,  well-pre- 
served forms,  showing  inner  markings. 
One  large  specimen,  somewhat  flattened, 
was  preserved  in  a  coat  of  wad,  a  replace- 
ment of  the  cortical  layer  probably  after 
carbonate  of  lime.  This  stem  lav  nearly 
east-west,  as  did  others  in  the  same  quarry,  biit  the  plants  are  disseminated 
and  occur  at  no  particular  level,  indicating  the  occasional  drifting  in  of 
floating  trees  and  the  rapid  accumulation  of  the  sands  and  pebbles. 

Sigillariaf  Long,  slightly  tapering,  flattened  stems,  with  longitudinal 
striations,  but  without  cross  markings,  occur  in  this  section,  usually  pre- 
served as  internal  casts  in  sandstone.     They  may  be  ill-preserved  calamites. 

In  the  rubbish  in  the  bottc  m  of  the  quarry,  but  evidently  transported, 
were  fragments  of  shale  with  raindrop  impressions. 

The  sandstone  beds  are  traversed  by  a  fault  striking  N.  44°  W.,  with 
a  hade  of  10°  S.,  and  the  well-marked  slickensides  have  a  uniform  pitch  on 
the  exposed  wall  of  55°  NW.  This  dislocation  can  not  be  of  any  consider- 
able extent,  for  the  same  sandstones  lie  on  both  sides  of  the  plane  of  divi- 
sion. Another  set  of  divisional  planes,  in  the  form  of  very  close-set  joints, 
striking  N.  46°  E.,  divides  the  sandstone  along  a  belt  of  variable  width  into 


Fig.  19.— Sketch  of  zone  of  excessively  jointed  s.ind- 
stones  (SS),  face  of  McCormick's  quarry. 


166  GEOLOGY  OF  THE  NAREAGANSETT  BASIN. 

blocks  too  small  for  building  purposes.  (See  fig.  19.)  This  zone  of  jointed 
rock  widens  from  not  more  than  2  feet  at  the  present  sui'face  to  10  or  12 
feet  at  a  depth  of  20  feet. 

Section  from  Watchemocket  Cove  to  Riverside. The  rOcks    wHch    appear  in  the    quar- 

ries  above  described  come  to  the  seashore  in  bold  clifi"s  between  Watche- 
mocket Cove  and  Riverside,  and  in  a  few  places  the  natural  section  has 
been  made  clearer  by  railway  cuts.  About  100  feet  in  thickness  of  Carbon- 
iferous sandstones,  conglomerates,  and  shales  are  exposed  along  this  section, 
in  the  form  of  a  broad,  flat  syncline  from  Watchemocket  Cove  to  near  Pom- 
ham  Rock,  where  the  strata  become  vertical  and  are  much  distm-bed,  at  one 
point  the  sandstone  beds  having  been  reduced  to  breccia.  The  strata  just 
south  of  Silver  Spring  form  terraces  overlooking  the  bay.  Northeastward 
from  Pomham  Rock  and  Riverside  the  same  strata  are  seen  inland  in  the 
three  ridges  indicated  on  the  topographic  map.  In  the  eastern  one  of 
these  long,  low  ridges,  the  sandy  conglomerates  dip  northwestward  at  a 
very  low  angle,  but  the  strata  in  the  westernmost  of  the  ridges  dip  steeply 
east,  being  along  the  line  of  the  Pomham  anticline.  Northeastward,  at  a 
point  about  a  mile  due  east  from  Vue  de  1'  Eau,  the  strata  turn  more  to  the 
eastward,  as  if  in  the  canoe  end  of  a  syncline.    (See  fig.  20.) 


Fig.  20 Geological  section  from  "V^^atclieraoctet  Cove  to  Riverside,  "Rliode  Island,  showing  the  attitude  of  the  Carbonifer- 
ous strata.  A,  Kettle  Point;  B,  Squantum;  C,  Silver  Spring;  D,  Pomham  Eock;  E,  Riverside;  F,  Outcrop  near 
Sherman  Station. 

South  of  Riverside  the  rocks  are  not  well  exposed.  The  details  of 
stratigraphy  along  this  shore  are  sufficiently  illustrated  in  the  following 
notes : 

Halsey  Farm  section  at  Silver  Spring. A     feW    rods    SOUtll   of    SilvCr    SpHug    StatloU 

the  following  section  was  measured  in  the  bluff"  at  Halsey  Farm: 
Section  in  bluff  near  Silver  Spring  Station,  Rhode  Island. 

Feet. 

Sandstone  and  conglomerate  (at  top) 40 

Conglomerate  with  pebbles  of  quartzite  and  granite 6 

Sandstone  (to  bottom) 4 

These  strata  are  approximately  horizontal,  but  farther  east  they  dip 
eastwardly,  and  westward  across  the  railroad  track  they  dip  as  high  as 


KHODE  ISLAND  COAL  MEASURES. 


167 


45°  E.     In  the  railway  cut  the  same  series  of  strata  show  a  north-south 
vertical  fault  plane,  the  slickensid.es  of  which  are  horizontal.      There  is 


Pig.  21 Geological  section  through  rocky  islets  at  Halsey  Farm,  Silver  Spring,    a,  the  rooky  head  shown  in  PI.  VI; 

R.  R.,  the  railroad. 

present  a  coarse  slaty  cleavage,  but  it  is  not  a  constant  feature.  The 
joint  planes  display  great  feathery  surfaces  of  fracture,  the  divergent 
lines  of  which  indicate  the  direction  of  splitting;  this  sometimes  is  upward 
or  downward,  but  very  frequently  in  a  horizontal  direction,  the  plane  being 
vertical.  With  certain  precautions,  the  dip  of  massive  beds  can  be  obtained 
by  observing  the  inclination  of  the  axes  of  these  feather  fractures.  The 
joint  planes  frequently  die  out  with  a  convex  front,  the  periphery  being  cast 
into  concentric  flexures  of  conchoidal  fracture,  often  measuring  an  inch  from 
trough  to  crest.  These  planes  of  fracture  exhibit  splitting  figures  having  a 
length  of  at  least  6  feet  from  the  rather  indistinct  point  of  origin  to  the 
sharply  incised  marginal  rugosities.-^ 

A  few  rods  farther  south,  but  north  of  Pomham  Rock,  is  a  small  rocky 
headland,  composed  of  two  distinct  ridges,  in  which  the  following  section 
was  shown,  dipping  45°  E.,  the  same  rocks  reappearing  in  the  islets  north- 
ward by  the  Silver  Spring  shore. 

b  o 

c 


Fio. 22.— Geological  section  of  rocky  headland  below  JiaUuy  larni  .;Uijir,  mar  Silver  Spring,  Rhode  Island.    (For  expla- 
nation of  letters,  see  accompanying  section.) 

Section  in  rocky  headland  near  Silver  Spring  Station,  Rhode  Island. 

Feet. 

e.  Slate  (at  top) 15 

d.  Grits 15 

c.  Slates,  partly  covered 25 

b.  Grits  and  sandstones,  with  pebbles,  isolated,  and  in  bands  and  pockets 15 

a.  Slates  with  sandy  layers,  showing  local  unconformity  to  b,  due  to  couteinpo- 
raneous  erosion;  plant  stems  occur,  and  the  upper  portion  of  the  bed  is  car- 
bonaceous ;  cross  bedding  very  marked ;  exposed  above  high-tide  mark 6 

'  For  a  detailed  description  of  this  type  of  fractures,  see  paper  "On  the  fracture  system  of  joints, 
ate,"  by  the  author :  Proc.  Boston  Soc.  Nat.  Hist.,  Vol.  XXVII,  1896,  pp.  163-183, 


1,68 


GEOLOGY  OF  THE  IfAERAGAKSETT  BASIX. 


Fossils. — North  of  the  station  black  shales  contain  impressions  of  Sphe- 
nojihi/Uum  schlotheimii,  both  alone  and  with  Asterophyllites  equisetiformis. 
Pecopteris,  smaller  than  P.  unita,  also  occurs  here.  In  the  mudstones  on 
the  bluff  calamites  are  abundant. 

In  the  rocky  points  and  islets  along  the  shore  near  Silver  Spring  the 
dips  steepen  to  45°,  rising  to  an  anticline  arching  over  the  upper  narrow 
end  of  Narragansett  Bay — the  southward  continuation  of  the  fold  which  is 
more  clearly  indicated  by  the  outcrops  on  the  sides  of  the  Seekonk  River. 
The  southward  extension  of  this  anticline  is  not  readily  traceable.  The 
sandstones  and  conglomerates  reappear  in  the  ledge  at  the  present  mouth 

of  the  Pawtuxet  River,  and 
again  at  Rocky  Point,  on  the 
west  side  of  the  bay. 

It  is  evident  from  a  diag- 
nosis of  the  dips  in  Provi- 
dence and  East  Providence 
that  the  strata  in  this  section, 
from  the  western  boundary 
eastward  into  the  middle  of 
the  basin,  behave  very  much 
in  the  manner  of  the  layers 
under  horizontal  pressure  in 
the  clay  models  experimented  upon  by  Mr.  Bailey  Willis.^  The  general 
structure  of  a  cross  section  from  back  of  Providence  southeastward  to 
Riverside  is  represented  in  the  accompanying  diagram,  fig.  23.  It  will  be 
noticed  that  there  is  a  belt  of  A^ery  highly  tilted  strata  next  the  resisting 
pre-Carboniferous  teiTane,  in  which  the  effects  of  great  pressure  are  mani- 
fest also  by  the  degree  of  metamorphism ;  thence  eastward  lies  a  belt  of 
little-distui'bed  strata  without  any  marked  metamorphism  or  even  slaty 
cleavage ;  there  come  in  then  subordinate  anticlines  with  a  slight  amount  of 
rock  crushing.  These  two  anticlinal  axes  correspond  to  what  Mr.  Willis 
terms  consequent  and  subsequent  anticlines,  respectively. 

It  is  a  noticeable  feature  of  many  of  the  folds  in  this  part  of  the  basin 
that  the  inclination  of  the  strata  increases  to  a  maximum  near  the  axis. 


Fig.  23.— Theoretical  section  of  folded  .structure  on  western  margin  of  the 
Narragansett  Basin,  a,  Providence  anticlinal  belt;  fc,  East  Providence 
flat  syncline;  c,  Pombam  Rock  anticline.  (See  PI.  LXXXII,  figs,  f-i, 
Thirteenth  Ann.  Kept.  U.  S.  Geol.  Survey,  Part  II.) 


'The  mechanicB  of  Appalachian  structure:  Thirteenth  Ann.  Rept.  U.  S.  Geol.  Survey,  Part  II, 
1893,  PI).  211-289. 


EHODE  ISLAND  COAL  MEASUEBS.  169 


EXPOSURES  IN  THE  TOWN  OF  SEEKONK. 


The  lowest  strata  exposed  in  this  town  occur  along  the  east  bank  of 
Tenmile  River. 

Section  at  Hunts  Mills. — In  December,  1892,  a  pit  was  sunk  into  the  bed  of 
the  stream  at  this  point  for  the  installation  of  a  turbine  water  wheel.  A  bed 
of  coal  in  the  following  stratigraphic  position  was  penetrated,  the  overlying 
beds  being  exposed  in  the  banks  of  the  river: 

Section  at  Hunts  Mills,  Rhode  Island. 

Feet, 

Sandstone,  of  the    graywacke  type.     Near  tbe  falls  are  large  impressions  of 

unideutifled  plant  stems 40 

Conglomerate,  medium-sized  pebbles,  quartzose 5 

Sandstone 10 

Goal,  anthracitic,  showing  slickensides,  local  crushing,  and  gash  veins,  with  a 
white  asbestiform  mineral 3i 

Shale,  black,  varying  from  a  fine-grained  compact  argillite  to  an  arenaceous  rock; 
thickness  unmeasured. 

These  strata  dip  gently  to  the  north  of  east.  The  coal,  uniformly  like 
that  on  the  east  side  of  the  Seekonk  River,  is  much  less  graphitic  and 
altered  than  that  which  comes  from  the  west  of  that  line  in  the  metamor- 
phosed belt.  It  is  granular  and  is  traversed  by  small  quartz  and  calcite 
veins.  The  strike  of  this  bed  would  carry  the  coal  along  the  present  path 
of  the  Tenmile  River  northward  for  several  miles.  No  attempt  has  been 
made  to  use  this  coal  or  to  explore  the  underlying  shales  at  other  points  in 
this  vicinity  for  other  like  deposits. 

North  of  Hunts  Mills,  and  about  a  mile  south  of  Lebanon  Mills,  a 
heavy -bedded  sandstone  crops  out  on  the  east  bank  of  the  river. 

In  the  northern  part  of  the  town,  strata  approximately  on  the  horizon 
of  the  Tenmile  River  beds,  and  subjacent  thereto,  have  been  explored  for 
coal.  One-fourth  of  a  mile  east  of  Perrins  Station,  on  the  Fox  Point  Rail- 
road, is  an  outcrop  of  conglomerate  and  sandstone  near  the  horizon  of  the 
upper  part  of  the  Hunts  Mills  beds. 

Perrins  anticline. — Between  Perrius  and  East  Junction,  in  the  cut  on  the 
railroad  to  Fox  Point,  is  an  anticlinal  exposure  of  the  lowest  beds  seen  in 


170  GEOLOGY  OF  THE  NAliRAGANSBTT  BASIN. 

Seekonk.  The  axis  of  this  fold  is  probably  that  also  of  the  great  anticline 
which  lies  between  the  Attleboro  syncline  and  the  Great  Meadow  Hill  svn- 
cline.  The  axial  plane  is  overturned  to  the  north.  On  the  northern  side  of 
the  cut,  sandstones  and  conglomerates  dip  NNW.  at  an  angle  of  45°;  in 
the  southern  half,  sandstone  beds  with  fossiliferous  shales  dip  SSE.  at 
angles  from  30°  to  15°.  There  are  no  exposures  at  the  point  where  the 
anticlinal  strata  would  be  expected  to  connect  the  two  parts  of  the  section 
in  an  arch,  and  evidence  of  an  overthrust  is  wanting. 

Fossils. — Several  species  of  plants  have  been  found  in  a  good  state  of 
preservation  in  the  shales.  The  fronds  of  a  species  of  Odontopteris  are 
usually  graphitized  and  shining.  One  layer  in  the  sandstones  is  covered 
with  the  impressions  of  large  Pecopteris  fronds  matted  together,  but  show- 
ing the  spore  cases.  The  following  fossils  were  found  at  this  locality: 
Cordaites  sp.,  Pecopteris  unita,  Odontopteris  sp..  Catamites  sp. 

Bored  well  near  Lebanon  Mills. — About  half  a  milc  west  of  thc  fossilifcrous  beds 
above  described,  on  the  land  of  Mr.  L.  W.  Bourn,  a  boring  was  made 
about  fifteen  years  ago.  The  hole  reached  a  depth  of  705  feet  4J  inches, 
the  surface  of  the  ground  being  about  90  feet  above  sea  level.  The  upper- 
most stratum  underlies  the  shale  section  in  the  Perrins  anticline.  The 
following  strata  were  passed  through,  according  to  a  copy  of  the  record  in 
the  possession  of  Professor  Shaler: 

Geological  column  of  diamond-drill  hole  made  for  the  Seekonlc  Goal  Mining  Gompany 
on  their  anthracite  coal  lands,  Bristol  Gounty,  Massachusetts,  under  the  direction  of 
Thos.  S.  Bidgipay,  geologist  and  mining  engineer. 

Feet.  Inches. 

Sand,  gravel,  and  bowlders 54      0 

Argillaceous  slate,  containing  impressions  of  coal  plants 4      0 

Siliceous  grit,  alternating  with  argillaceous  slates 13      6.  5 

Graj'  sandstone,  micaceous,  flue  grained 9      9 

Gray  sandstone,  coarse  and  flue,  alternating  with  red,  bluish,  purple,  and 

olive-colored  variegated  shales 34      4 

Sandstone,  compact,  bluish,  containing  seams  of  slate 17      4 

Gray  grit  rock  and  sandstone,  micaceous  slates  alternating 18  10 

Bluish  sandstone,  micaceous,  alternating  with  rock  binds;  lower  part  shaly, 

containing  impressions  of  coal  plants 17      0 

Gray  micac>  ous  sandstones,  with  layers  of  grit  rock  and  slate V2      9 

Argillaceous  rock  and  thin  beds  of  sandstones  with  seams  of  slate 9  10 


EHODE  ISLAND  COAL  MEASURES.  171 

Oeological  cokimn  of  diamond-drill  hole  made  for  the  Seelconk  Goal  Mining  Company 
on  their  anthracite  coal  lands,  etc. — Continued. 

^eet.  luches. 

Argillaceous  rock,  variegated,  lower  part  thin  layers  of  slate 12  0 

Bluish  sandstone 8  0 

Sandstone,  mustard-seed  grit 24  0 

Compact  gray  sandstone 7  4 

Slate  and  sandstone  alternating 8  6 

Sandstone  and  grit  alternating,  mustard-seed  grit 12  9 

Sandstone,  coarse  and  fine,  micaceous,  thin  seams  of  slate 8  4 

Argillaceous  slates  containing  thin  seams  of  coal  and  impressions  of  plants.     9  4. 5 

Coarse  and  fine  micaceous  sandstones  (depth,  288.5  feet) 6  9. 5 

Conglomerate - 32  4 

Eed  conglomerate  rock;  slate  containing  streaks  of  coal;  Gray  sandstones 

and  coal  slates  alternating 8  3 

Gray  sandstones,  coarse  and  fine  micaceous,  separated  by  argillaceous  binds .  22  3 

Rock  binds  and  sandstones  containing  veins  of  quartz 18  0 

Coal  slates  containing  impressions  of  coal  plants  ;  lower  parts  dark  sand- 
stone       7  7 

Gray  sandstone  and  argillaceous  rock 8  0 

Dark-colored  sandstone  and  carbonaceous  slate 7  0 

Sandstone,  micaceous,  and  coal  slates  containing  impressions  of  coal  plants.  10  0 

Coarse  sandstone,  micaceous 8  10 

Coarse  sandstone,  lower  part  containing  thin  seams  of  anthracite;  sandstone, 

micaceous  and  conglomeratic 14  5 

Conglomerate  (depth,  425.15  feet) 7  0 

Gray  sandstone,  micaceous 13  4 

Conglomerate 4  9 

Gray  sandstone  and  slate 3  11 

Gray  sandstone,  micaceous,  containing  slate  with  plant  impressions 8  2 

Sandstone  and  slate,  alternating,  containing  thin  seams  of  coal 4  7 

Fine- grained  sandstone  containing  thin  seams  of  slate  and  coal  with  impres- 
sions       5  3 

Coal  slates  containing  coal  plants;  upper  part  sandy  (depth,  479.15  feet). . .     7  8 

Gray  sandstone,  fine  grained,  micaceous 13  6 

Dark-gray  grit  rock 7  9 

Slate  and  sandstone,  2  feet;  dark-gray  grit,  3  feet  4  inches;  sandstone  and 

seam  of  slate,  3  feet  3  inches 8  7 

Gray  sandstone,  3  feet  5  inches;  binds,  6  feet  7  inches 10  0 

Gray  sandstone .  -  - 6  6 

Binds,  2  feet  7  inches;  slate  containing  plant  impressions;  supposed  thin 

seam  of  coal,  2  feet  6  inches  (depth,  531  feet  2.5  inches) 5  1 


172  GEOLOGY  OF  THE  NAERAGANSETT  BASIN. 

Geological  column  of  diamond- drill  hole  made  for  the  Seekonl:  Coal  Mining  Comimny 
on  their  anthracite  coal  lands,  etc. — Continued. 

Feet.   Inches. 

Coal  slates  with  impressions,  2  feet  2  inches;  sandstone  and  slates  alternat- 
ing, G  feet  6  inches 8  8 

Gray  sandstone,  micaceous,  fine  grained  and  variegated 48  10 

Slate,  2  feet  7  inches;  dark-colored  sandstone,  4  feet  6  inches;  supposed 

thin  seam  of  coal,  1  foot  8  inches  (dei)th,  597  feet  5.5  inches) 8  9 

Dark-colored  micaceous  sandstone - 7  5 

Slate  containing  streaks  of  coal 4  7 

Dark-gray  micaceous  sandstone  and  slate 11  8 

Carbonaceous  slate  and  trace  of  coal,  9  inches;  fine-grained  sandstone  and 

slate,  2  feet  4  inches  (depth,  621  feet  1.5  inches) 3  1 

Brownish  micaceous  sandstone - 5  3 

Slate  and  sandstone 6  4 

Dark-colored  micaceous  sandstone  and  slate  containing  calc  spar  in  veins. .  8  11 

Slate  containing  impressions  of  coal  plants 7  9 

Gray  and  brownish  sandstones 7  10 

Gray  sandstone  with  bands  of  slate 7  9 

Sandstone  and  slate 5  3 

(Unnamed  rock) 6  7 

Slate  and  sandstone 8  5 

Dark-gray  sandstone,  top  roof,  7  feet  6  inches ;  carbonaceous  slates  containing 

impressions  of  coal  plants,  9  feet  9  inches 17  1 

Bed  of  anthracite  coal  ("?).     (See  statement  below.)     (Depth,  700  feet  7.5 

inches.) 8  11 

Slate  containing  vegetable  impressions 4  9 

The  coal  bed  reported  in  the  above  table  at  the  bottom  of  the  hole  is 
said  to  have  been  a  fraud.  According  to  Dr.  Arthur  B.  Emmons,^  "no  coal 
core  was  ever  cut  in  the  hole,  and  the  coal  core  exhibited  as  having  been  so 
cut  was  cut  at  the  top  of  the  hole  from  a  piece  of  coal  brought  onto  the 
ground  for  the  purpose." 

In  June,  1895,  I  visited  the  locality,  and  from  an  examination  of  some 
of  the  cores  then  obtainable  on  the  place  was  able  to  make  out  the  dip  of 
the  beds  as  varying  from  10  to  15  degrees,  figures  which  agree  with  the 
southward  dips  of  the  strata  on  the  same  strike  line  in  Perrins  railway  cut. 
The  red  conglomerate  which  appears  at  a  depth  of  320  feet  is  suggestive  of 
the  reappearance  of  members  of  the  Wamsutta  series ;  but  from  a  comparison 
of  the  section  of  this  portion  of  the  Coal  Measures  it  is  difficult  to  conceive 

'Trans.  Am.  Inst.  Mln.  Eng.,  Vol.  XIII,  1885,  p.  517. 


EHODE  ISLAND  GOA.L  MEASURES.  173 

that  all  the  red  beds  lying  on  the  outskirts  of  the  great  Wamsutta  mass 
belong  on  the  same  horizon.  In  a  red  slate  core  there  could  be  seen 
annelid  casts,  such  as  characterize  the  red  slates  on  the  south  side  of  the 
Attleboro  syncline  (see  p.  178).  It  is  to  be  noted  also  that  about  1  mile 
northeast  of  Perrins  cut  the  red  series  is  exposed  in  the  northeast  comer  of 
the  town  of  Rehoboth.     Red  shales  here  also  contain  annelid  tubes. 

The  stratigraphic  thickness  of  the  boring,  on  the  doubtful  assumption 
of  the  parallel  dip  of  the  beds  to  the  bottom,  is  about  628  feet.  There  are 
upward  of  1,800  feet  of  measures  to  the  highest  exposures  just  above  the 
Seekonk  conglomerate,  and  there  are  upward  of  2,000  feet  of  concealed 
measures  from  this  horizon  upward  to  Great  Rock,  where  coarse  conglom- 
erates, supposed  to  be  of  the  Dighton  horizon,  come  in.  This  calculation 
gives  the  group  of  Coal  Measures  below  the  Dighton  conglomerate  in  this 
section  a  minimum  thickness  exceeding  5,000  feet.  If  5,000  feet  of  strata 
below  the  Dighton  conglomerate  are  measured,  in  the  tyj^ical  area  on  either 
side  of  the  synclinal  axis  in  Dighton  and  Swansea,  it  will  appear  that  the 
bottom  of  the  series  is  here  by  no  means  reached.  I  am  therefore  led' to 
place  the  beds  just  described  relatively  high  up  in  the  Coal  Measures. 

SEEKONK   BEDS. 

About  a  mile  east  of  the  Tenmile  River  beds,  and  about  1,000  feet 
higher  up  stratigraphically,  is  a  series  of  monoclinal  ridges  of  sandstone 
and  conglomerate  which  afford  the  best  natural  exposition  of  the  Carbon- 
iferous strata  that  is  found  anywhere  in  the  inland  portion  of  the  basin. 
While  sandstones  form  the  dominant  exposures  and  leading  topographical 
feature  of  this  series,  shales  enter  about  equally  into  the  thickness  of  the  beds. 

West  and  south  of  the  farm  of  Mr.  Davis  Carpenter  these  arenaceous 
and  gritty  rocks  rise  from  20  to  30  feet  in  height,  in  an  area  of  about 
1  square  mile,  in  five  principal  ridges,  striking  a  few  degrees  E.  of  N.  and 
dipping  E.  from  20°  to  30°.  The  aggregate  thickness,  including  sandstone 
and  shale  below  a  thick  conglomerate  bed,  is  somewhat  less  than  2,000  feet. 
There  is  no  evidence  to  show  that  the  successive  ridges  are  due  to  the  repe- 
tition of  step  faults  bringing  up  a  single  bed.  East  of  the  stream  on  the 
Woodard  place,  in  the  southeastern  part  of  the  area  of  exposures,  a  sand- 
stone ridge  has  been  quarried,  the  strata  here  affording  rough,  thick  flags. 
The  large  strike  joints  which  occur  here  are  very  smooth  and  nearly  ]3ar- 


174  GEOLOGY  OF  THE  NARRAGANSETT  BASIN. 

allel,  but  the  dip  joints  are  much  less  regular  planes.  One-fourth  of  a 
mile  west  of  this  locality  there  is  a  long  ridge  of  alternating  grits  and 
conglomerates,  probably  the  outcrop  of  the  heavy  conglomerate  which 
comes  in  more  distinctly  farther  north.  The  beds  are  penetrated  by  nests 
and  veins  of  white  quartz.  In  the  shales  underlying  one  of  the  sandstone 
ridges  impressions  of  calamites  and  asterophyllites  were  found  in  the  course 
of  the  present  survey  by  Mr.  W.  E.  Parsons. 

seekonk  conglomerate. — North  of  tliis  area,  about  a  mile  along  the  strike, 
the  geological  structure  and  topographical  features  are  repeated.  The  See- 
konk conglomerate  bed  here  becomes  more  pronounced  and  can  be  traced 
along  the  east  bank  of  a  small  brook  for  the  distance  of  a  mile.  It  is  from 
50  to  60  feet  thick,  very  massive,  and  contains  quartzite  pebbles  from  3  to 
6  inches  in  diameter.  Where  weathered  the  pebbles  fall  out  of  the  matrix 
readily  and  show  little  or  no  dynamic  metamorphism.  The  resemblance 
of  this  bed  to  the  conglomerates  of  the  Dighton  group  is  very  striking,  and 
the  bed  may  be  tentatively  considered  the  equivalent  of  the  coarse  con- 
glomerate which  occurs  at  the  base  of  this  group.  It  is  so  represented 
on  the  map. 

The  strata  in  the  northern  part  of  Seekonk  turn  northeast,  and  then 
due  east  and  pass  into  Rehoboth,  and  so  continue  on  to  the  tract  mapped 
on  the  Taunton  quadrangle.  Very  good  exposures  may  be  seen  along  the 
road  about  half  a  mile  north  of  the  head  of  Wolf  Plain  Brook.  A  coarse 
conglomerate  north  of  the  road  in  the  edge  of  the  woods  is  probably  the 
continuation  of  the  Seekonk  conglomerate.  It  is  overlain  by  sandstones 
and  pebble  beds  which  dip  from  5°  fo  10°  S. 

The  strata  just  described  in  Seekonk  and  in  the  northern  part  of 
Rehoboth,  as  shown  on  the  Providence  quadrangle,  form  the  western  part 
of  a  broad,  square-ended  syncline.  About  3  miles  south  of  the  point  where 
the  Seekonk  beds  turn  from  northerly  to  easterly  strikes  they  again  strike 
eastward  to  make  the  southern  side  of  the  Great  Meadow  Hill  syncline. 
Some  minor  folding  appears  between  this  point  and  Great  Rock. 

The  southern  part  of  Seekonk  and  Rehoboth  is  heavily  drift  covered, 
and  outcrops  are  from  2  to  3  miles  apart  and  not  in  sufficient  number  to 
give  much  value  to  the  interpretation  of  the  structure  in  this  part  of  the 
field.  About  2  miles  south-southeast  from  the  Davis  Carpenter  place  a 
coarse   conglomerate   striking   E.-W    and  dipping   80°   N.  comes  in,  over- 


EHODB  ISLAND  COAL  MEASURES.  175 

lying  sandstones,  indicating  the  abrupt  turning  of  the  strata  eastward  in 
the  manner  above  referred  to.  Half  a  mile  east  and  a  little  north  of  this 
outcrop,  coarse  pebbly  grits  dip  gently  S.,  indicating  minor  folds  in  this  part 
of  the  tield.  Whether  these  exposures  are  reappearances  of  the  Seekonk 
conglomerate  and  the  associated  thick  sandstones  is  an  open  question. 
The  general  structure  of  the  area  would  place  the  strata  at  the  top  of  the 
Seekonk  beds,  and  they  are  so  indicated  on  the  map. 

Three  miles  due  south  of  thpse  outcrops  are  two  isolated  outcrops  of 
gray  and  locally  pebbly  sandstone.  The  westerly  one  forms  a  low  roche 
moutonnee  on  the  land  of  Mr.  Fred.  T.  Haskins;  the  eastern  one,  at  the 
corner  of  the  road,  forms  a  massive  knob  25  feet  high.  In  the  southeastern 
corner  of  the  area  represented  on  the  Providence  atlas  sheet,  in  Swansea 
and  partly  in  Barrington,  Rliode  Island,  are  outcrops  of  sandstone  and 
conglomerate  striking  NNE.-SSW.  and  standing  at  high  inclinations.  At  a 
few  points  the  sandstones  rise  into  knobs  30  feet  high.  A  slaty  cleavage 
is  sometimes  shown  striking  N.  56°  W.  and  dipping  N.  Where  pebbles 
occiir  they  vary  from  half  an  inch  to  an  inch  in  diameter.  Between 
these  beds  and  the  last-described  outcrops  there  lies  the  broad,  shallow 
valley  of  the  Warren  River,  partly  drift  filled  and  indicating  the  existence 
of  some  underlying,  softer,  valley-making  beds  along  the  median  or  anti- 
clinal line  between  the  Dighton  and  Taunton  synclines. 

BEDS  NORTH  OF  THE  TENMILE  RIVER  IN  ATTLEBORO. 

Thus  far  there  have  been  described  a  series  of  strata  continuous  along 
their  strikes  on  the  south  and  east  of  the  Tenmile  River  and  along  the 
Providence  River,  and  a  section  upward  to  the  coarse  conglomerates  of  the 
Dighton  group.  Similar  strata  are  less  perfectly  shown  in  Attleboro  north 
of  the  Tenmile  River  and  the  Perrins  anticline.  On  the  south  side  of  the 
stream  and  the  axis  named  the  beds  dip  gently  southward,  but  wherever 
they  appear  on  the  north  they  have  steep  northerly  dips.  On  the  grounds 
of  the  American  Millenium  Association,  near  Hebronville,  a  well  was  sunk 
10  feet  in  drift  and  20  feet  into  a  gritty  sandstone,  but  the  first  ledges  of 
diagnostic  value  appear  along  the  banks  of  the  Tenmile  River  in  Dodge- 
ville,  where  sandstones  are  seen  dipping  steeply  northward.  Half  a  mile 
west  of  the  railroad  station,  and  over  2,000  feet  below  the  coarse  conglom- 
erate in  the  Attleboro   syncline,  is   an  isolated  exposure  of  coarse  gray 


176 


gp:ology  of  the  narragansett  basin. 


conglomerate  dipping-  70°  N.  About  60  feet  of  beds  are  exposed,  showing 
alternations  with  sandstone  and  slate.  The  pebbles  of  the  conglomerate 
are  granitite,  quartzite,  and  quartz,  and  range  up  to  6  inches  in  diameter. 
This  bed  occupies  a  stratigraphic  position  on  the  north  side  of  the  Perrins 
anticline  roughly  corresponding  to  that  of  the  Seekonk  conglomerate  on 
the  south  side  of  the  axis,  and  raises  the  question  whether  the  Seekonk 

conglomerate  is  the  coarse  con- 
glomerate elsewhere  found  at 
the  base  of  the  Dighton  group 
or  a  lower  conglomerate  com- 
pi'ised  within  the  Seekonk  beds 
proper.  Westward  and  east- 
ward for  many  miles  no  rocks 
are  exposed  along  this  northern 
strike  line. 

Somewhat  higher  up  in  the 
section,  and  over  a  mile  north- 
east of  the  last-named  outcrop, 
there  are  exposed,  along  the 
Old  Colony  Railroad  tracks  at 
Thatcher  road  bridge,  1  mile 
south -southwest  of  Attleboro 
station,  about  40  feet  of  coarse, 
gray,  gritty,  and  often  con- 
glomeratic sandstones  exhibit- 
ing cross  bedding  and  marked 
local  or  contemporaneous  ero- 
sion. A  bed  of  fine  sandstone 
20  feet  thick  was  excavated, 
evidently  by  a  river,  to  the  un- 
derlying coarse  pebbly  beds,  and  then  the  area  was  covered  up  with 
coarse  sands.  This  feature  can  be  relied  upon  to  show  that  the  northern 
face  of  the  strata  was  originally  uppermost.  The  beds  stand  at  high  angles, 
dipping  north. 

Contact  of  red  and  gray  beds,  with  local  unconformity. CrOSslug    UOrthward    OVCr  a  feW 

feet  of  covered  beds,  we  find  a  glaciated  exposure  by  the  roadside  exhib- 


Fig.  24. — Contemporaneous  erosion,  with  unconformity,  in  the  Car- 
boniferous at  Attleboro,  Massachusetts.  The  pebbles  shown  in 
the  upper  part  of  the  diagram  are  identical  with  the  red  slate  in 
the  lower  part. 


EHODE  ISLAND  COAL  MEASURES.  177 

iting  a  clear  instance  of  local  erosion  following  the  deposition  of  red  shales 
and  preceding  the  deposition  of  more  gray  beds.  Angular  fragments  of 
the  red  shale  occur  in  the  overlying  gray  beds,  completing  the  evidence  of 
unconformity  at  this  point.  The  structure  is  indicated  in  the  accompanying 
diagram  of  the  locality  (fig.  24). 

A  few  feet  stratigraphically  below  this  level  of  contemporaneous 
erosion  and  a  few  yards  westward  in  the  vertical  beds  is  the  well-marked 
unconformity  before  ixientioned.  It  is  partly  concealed  by  glacial  gravels, 
but  shows  the  cutting  off  on  the  west  of  about  20  feet  of  fine  sandstones. 
The  continuation  of  these  beds  on  the  west  of  this  ancient  channel  of 
erosion  is  not  exposed.  The  excavation  or  channel  thus  formed  was  subse- 
quently filled  with  coarse  sands,  which  also  mantle  over  the  fine  sandstones 
to  the  eastward  of  the  ancient  stream  bank. 

The  phenomena  of  this  horizon  indicate  clearly  the  fluviatile  nature 
of  the  sedimentation  in  this  portion  of  the  Carboniferous  area.  The  deposits 
may  have  accumulated  near  sea  level,  but  under  conditions  in  which  the 
streams  were  given  steep  gradients  and  large  supplies  of  freshly  eroded 
detritus  of  granite  and  quartzite,  as  if  in  some  mountainous  lake  or  bhabar 
district,  such  as  that  at  the  southern  base  of  the  Himalayas  in  India. 

Red  shales. — TliB  red  slialcs  which  now  succeed  the  gray  beds  can  be 
traced  southwestward  along  the  southern  side  of  the  Attleboro  syncline. 
They  alternate  with  gray  sandstones,  and  where  most  distinctly  shown  have 
an  ascertained  thickness  of  60  feet.  Strata  which  exhibit  a  reddish  color, 
however,  continue  upward  in  the  section  nearly  to  the  base  of  the  coarse 
conglomerate  which  forms  the  nose  of  the  syncline.  On  the  land  of  Mr. 
Joseph  Fisher  the  following  section  is  exposed: 

Section  near  Attleboro,  on  Thatcher  road. 

Feet. 

Eed  shales  aud  sandstones  with  gray  sandstone  interlaininated  (top  not  seen) 22 

Sandstone,  gray 8 

Sandstones,  grayish-green  (quarried) 52 

The  red  sandstones  contain  annelid  borings. 

A  little  higher  up  than  these  red  strata  is  a  coarse  conglomerate.  Still 
higher  up  are  fine  conglomerates  with  pebbles  of  quartzite,  granitite,  and 
quartz.  (See  PI.  VIII.)  The  quartz  is  often  deeply  stained  with  iron  oxide. 
Overlying  these  fine  conglomerates  are  the  reddish-tinged  strata  mentioned 

MON  XXXIII 12 


178 


GEOLOGY  OF  THE  NARRAGANSETT  BASIN. 


above.  At  the  eastern  end  of  the  syndine  shown  upon  the  map  these  beds 
mav  be  seen  turning  northward  and  westward,  with  cross  bedding  plainly 
showing  the  original  top  of  the  strata.  The  use  of  cross  bedding  in  deter- 
mining the  original  position  of  strata  depends  upon  the  fact  that  where  the 
inclined  "fore  set"  layers  are  somewhat  eroded  the  succeeding  layers  rest 
upon  their  truncated  edges.  The  evidence  thus  derived  from  the  cross 
bedding  confirms  the  view  that  these  beds  are  on  the  northern  side  of  an 
anticline  whose  axis  is  shown  in  the  Perrius  cut. 

These  beds  immediately  below  the  coarse  conglomerate  also  exhibit 
worm  burrows,  trails,  and  current  marks  (see  PI.  IX),  and,  what  is  even 
more  remarkable  for  this  basin,  the  imprint  of  raindrops  on  an  ancient 
beach  or  exposed  flat.     (See  PI.  X.) 

Raindrop  imprints. — The  locality  exhibiting  raindrop  imprints  is  about  one-half 
mile  southwest  of  the  crossroads  at  the  canoe  end  of  the  Atlleboro  syncline, 

where  the  reddish  micaceous 
sandstones  below  the  Dighton 
conglomerate  are  exposed  in  a 
quarry.  The  surface  of  one 
la3'er  is  current-marked,  with 
the  steep  fronts  of  the  irregu- 
lar ridg'es  facing  southeast 
when  oriented  with  reference 
to  the  horizontal  position,  the 
beds  now  standing  vertical  at  this  locality.  Over  the  current  marks  are 
the  imprints  of  raindrops.  These  records  of  former  meteorological  condi- 
tions are  on  the  northern  and  upper  face  of  the  vertical  bed,  and  the 
stratum  is  on  the  south  side  of  the  axis  of  the  syncline,  a  position  in  every 
respect  consistent  with  the  interpretation  of  the  stratigraphic  succession 
advocated  in  this  report.  This  is,  so  far  as  I  am  aware,  the  only  locality 
in  the  basin  in  which  raindrop  imprints  may  be  seen  in  situ.  The  preserva- 
tion of  the  record  at  this  locality,  where  the  beds  have  been  pushed  up  into 
a  vertical  attitude,  indicates  that  at  least  locally  the  dynamic  metamorphism 
in  the  Rhode  Island  coal  field  has  not  gone  so  far  as  has  been  commonly 
believed.  The  condition  of  the  imprints  in  this  case  further  shows  that  in 
the  folding  of  the  strata  there  was,  at  least  on  this  horizon,  little  or  no  wide- 
spread shearing  of  layer  over  laj^er,  an  action  which  in  other  localities  is 


Fig.  25. — Diagram  showing  cross  bedding.  A,  B,  successively  deposited 
layers  of  cross  bedding,  or  "fore-set"  layers ;  C,  later  layers,  covering 
the  eroded  surface  of  A,  B ;  a,  a,  a,  a,  erosion  surfaces. 


RAINDROP    IMPRINTS   AND    WORM    BURROWS   ON    VERTICAL   CARBONIFEROUS   STRATA,   SOUTH    FLANK   OF 
ATTLEBORO   SYNCLINE. 

Looking  somh.     Scale  m  inches. 


RHODE  ISLAND  COAL  MEASURES.  179 

usually  marked  by  miuute  slickensides  or  the  appearance  of  a  "grain" 
running  up  and  down  the  dip  in  the  direction  of  the  shearing  movement.  A 
slickensided  fault  plane  in  the  bedding  is  shown  at  this  locality. 

Attieboro  synciine. — One  of  the  few  points  in  the  basin  where  the  struc- 
ture and  superposition  of  beds  are  exhibited  within  a  small  area  and  in  a 
satisfactory  manner  is  midway  between  Attieboro  and  South  Attieboro,  in 
the  elevation  known  as  Ides  Hill,  lying  between  the  Tenmile  River  and 
Fourmile  Brook.  In  this  area  of  not  over  2  square  miles  there  is  a  well- 
defined  synciine  in  the  Carboniferous  strata,  involving  in  the  axis  a  thick 
section  of  coarse  com^jound  conglomerates,  immediately  overlying  the 
highest  of  the  rocks  just  described  as  lying  north  of  the  Perrins  anticline. 
The  nose  of  this  synciine  is  formed  by  the  conglomerate,  which  stands  up 
as  a  low  bluff  at  the  crossroads  1^  miles  southwest  from  the  station  in 
Attieboro.  (See  PL  XII.)  The  beds  on  the  south  side  are  vertical,  and 
can  be  traced  along  the  entire  area  above  described.  The  corresponding 
strata  on  the  northern  side  of  the  synciine  are  not  so  well  exhibited.  Near 
the  crossroads  just  mentioned,  conglomerates  exhibit  a  southward  dip  of 
about  45°,  and  about  2  miles  west,  near  Fourmile  Brook,  steep  southerly 
dips  are  again  seen  in  conglomerate.  Northward  to  the  edge  of  the  Wam- 
sutta  series  the  structure  is  not  exposed. 

It  seems  probable  that  this  group  of  conglomerates  belongs  on  the 
horizon  of  the  Dighton  group,  at  the  top  of  the  Coal  Measures  in  this  basin 
(see  p.  184),  the  red  rocks  of  the  Wamsutta  group  on  the  north  having  been 
brought  up  against  these  higher  beds  by  dislocation. 

Eastward  of  Attieboro  and  northward  to  the  limits  of  the  Providence 
quadrangle  in  the  directions  named,  the  surface  is  too  thickly  covered  with 
glacial  di'ift  to  make  an  interpretation  of  the  under  geology  possible.  The 
area  is,  I  confidently  believe,  underlain  by  Carboniferous  strata,  abundant 
fragments  of  grayish  conglomerates,  grits,  and  sandstones  occurring  in  the 
drift.  Judging  from  these  erratics,  which  have  not  traveled  far,  con- 
glomerates and  the  finer-grained  rocks  occur  in  this  tract.  The  red  Wam- 
sutta beds  may  also  be  expected  to  reappear  in  this  eastern  area,  folded  in 
with  the  gray  rocks.  Bowlders  of  this  formation  appear  in  the  glacial  drift 
northeast  of  Attieboro. 

Westward  of  the  line  of  section  above  described  there  are  two  or  three 
well-marked  knobs  of  sandstone  and  conglomerate  on  the  east  of  the  road 


180 


GEOLOGY  OF  THE  NAERAGANSBTT  BASIN. 


from  South  Attleboro  to  Hebronville.     These  beds  probably  represent  the 
horizon  of  the  Seekonk  group  on  the  north  side  of  tlie  Perrins  antichne. 


BLAKE  HILL  FAULT  BLOCK. 


The  gray  Carboniferous  strata  west  of  Plainville  in  Blake  Hill  exhibit 
several  small  monoclinal  ridges  of  hard  sandstone  and  quartzose  conglom- 
erate with  interbedded  shales,  here  and  there  containing  casts  of  calamites 
and  rarely  other  members  of  the  Carboniferous  flora.  The  most  prominent 
of  these  ridges  has  received  the  name  of  "Goat  Rock."  A  detailed  meas- 
urement of  the  strata  exposed  in  this  bluff  above  the  talus  has  been  made 
bv  Mr.  F.  C.  Schrader,  to  illustrate  the  character  of  the  barren  beds  in  this 
section : 

Section  of  Goat  EocJc  Cliff. 


Gray  sandstone  (at  top) 

Conglomerate,  gray,  coarse,  with  irregular  partings  of  black  slate  about 

2  feet  from  base  12 

Shale,  dark  and  slaty 

Sandstone,  gray,  varying  to  a  pebbly  grit 1 

Shale,  dark  and  slaty 

Sandstone,  gray,  with  a  few  small  pebbles  in  middle  of  the  layer 

Grit,  fine,  pebbly    

Sandstone,  grading  downward  from  above 

Sandstone,  hard,  fine  grained 

Shale,  slaty,  with  plant  stems 1 

Sandstone,  very  fine  grained 1 

Shale,  slaty 

Grit,  gray  and  finely  conglomeratic 

Shale,  dark  slaty 

Sandstone  and  grit - 

Conglomerate,  gray,  gritty,  and  grading  upward  into  next  above 

Sandstone,  gray 

Shale,  slaty 

Sandstone,  bluish  gray 

Shale,  black  and  slaty,  with  plant  stems 

Conglomerate,  flue,  gray,  and  gritty 1 

Shale,  dark  and  slaty,  a  mere  layer 

Sandstone,  gray 

Shale,  dark,  slaty 

Sandstone,  gray 


Feet.    Inches. 

9 


0 

8.5 

4 

2 
11.5 

3.5 

4 

5.5 
10 

1.5 

11.50 
11 
8.50 

7 


11 
3 

8 


EHODE  ISLAND  COAL  MEASUEES.  181 

Section  of  Goat  Bock  (7/i^— Continued. 

Peet.    Inolaes. 

Shale,  dark,  slaty,  a  mere  layer .2 

Sandstone,  gray 5.  5 

Shale,  with  fossils,  grading  into  sandstone 4 

Sandstone,  slaty , 6.  5 

Slate .75 

Sandstone,  a  hard  gray  rock 4. 5 

Grit,  gray  and  hard 9 

Sandstone,  gray,  with  plant  stems,  and  traces  of  finegrained  dark  slate  . .  2.  5 

Sandstone,  subslaty,  with  plant  stems :' 1 

Sandstone,  fine  grained,  gray 6 

Shale,  dark,  slaty,  trace .25 

Sandstone,  gray 3 

Shale,  dark  reddish  and  slaty,  with  plant  stems .75 

Conglomerate,  gray  and  gritty,  rather  line 2.  5 

Shale,  black  and  slaty,  with  plant  stems 8.  5 

Sandstone,  fine  grained,  dark  gray,  and  in  places  gritty .4 

Shale,  dark  and  slaty 5 

Sandstone,  gray 10 

Conglomerate,  fine  and  gritty 2+ 

Talus  of  covered  strata 30      0 

A  noticeable  feature  in  this  section  is  the  frequent  alternation  from 
sandstone  to  shales  within  a  very  limited  thickness.  The  coarse  conglom- 
erate forming  the  crest  of  the  ridge  exhibits  a  variety  of  pebbles,  as  regards 
both  origin  and  secondary  strtictures.  The  pebbles  are  chiefly  a  fine- 
grained whitish  quartzite,  often  presenting  slaty  cleavage,  the  discordant 
direction  of  which  structure  in  juxtaposed  pebbles  is  evidence  of  mountain- 
building  in  this  geological  province  prior  to  the  Carboniferous  period  and 
subsequent  to  the  formation  of  the  quartzite,  which  is  probably  of  lower 
Cambrian  age. 

Fossils. — The  fossils  found  in  place  in  this  section  are  mainly  imperfect 
stems  of  calamites.  In  the  drift  in  the  vicinity  of  Goat  Rock  there  have 
also  been  found  two  species  of  determinative  value,  viz:  Alethropteris  and 
Sigillaria  volzii  Bt. 

The  latter  plant  is  stated  by  Lesquereux^  to  be  rare  in  the  Coal 
Measures  of  America,  one  specimen  being  seen  by  him  from  the  Plymoutli 
F  vein  in   Pennsylvania,  a  horizon  near  the  top  of  the  anthracite  field. 

'  Coal  Flora,  p.  492,  PI.  LXXII,  fig.  11. 


182  G-EOLOGY  OF  THE  NAREAGANSETT  BASIN. 

Dr.  A.  F.  Foerste  also  found  in  the  sandstones  of  this  area  calamite  trunks 
6  inches  in  diameter. 

Coal. — A  bed  of  coal  said  to  be  6  feet  thick  was  met  with  in  digging  a 
well  on  the  land  of  Mr.  Charles  P.  Simpson  in  the  autumn  of  1890.  This 
locality  is  in  the  southern  part  of  Wrentham,  near  the  Attleboro  boundary 
line  and  on  the  eastern  face  of  Blake  Hill  block.  (See  PI.  XL)  The  well 
is  reported  to  have  passed  through  the  following  strata: 

Section  of  well  near  Attleboro,  Massaclmsetts. 

Teet. 

Sandstone 24 

Coal,  anthracite - 6 

"Flinty  sand  rock,"  thickness  unknown. 

Westwardly,  gray  conglomerates  ovei'lie  the  coal  section,  and  east- 
wardly  sandstones  crop  out  from  beneath  it.  It  is  shown  by  these  latter 
beds  that  the  dip  is  here  gentle  to  the  southwest.  The  outcrop  of  the  coal 
bed  is  about  260  feet  above  sea  level  and  from  20  to  25  feet  above  the  level 
of  the  pond  in  the  northwest  part  of  North  Attleboro.  Southward  of  this 
locality  the  Blake  Hill  block  is  probably  cut  off  by  a  fault,  as  basal  arkoses 
come  in  at  the  distance  of  half  a  mile  along  the  strike  line.  Northwestward 
along  the  strike  the  conditions  appear  favorable  for  exploiting  this  bed  along 
the  western  side  of  the  Plainville  Valley. 

Yet  farther  eastward,  and  lower  down,  micaceous  sandstones  crop  out 
along  the  roadside  and  contain  impressions  of  trees  of  small  size.  At  other 
points  along  the  southern  edge  of  the  Blake  Hill  block  the  waste  from 
highly  carbonaceous  shales  occtirs  in  the  glacial  diift. 

This  block  of  strata  dips  throughout  to  the  westward,  the  dip  increasing 
from  near  horizontality  along  the  eastern  boundary  at  Plainville  to  30°  and 
45°  along  the  western,  ill-defined  margin.  The  western  contact  is  appar- 
ently made  with  the  red  Wamsutta  series.  It  appears  as  if  this  block, 
over  a  mile  in  width  and  about  3  miles  in  length,  had  been  thrust  into  its 
relatively  undisturbed  position,  while  the  strata  around  it  on  the  east,  south, 
and  west,  as  well  as  the  beds  beneath  its  eastern  foot,  had  been  thrown  into 
steep  folds  and  even  overturned.  It  will  be  noted  that  the  Blake  Hill  block 
lies  north  of  and  behind  the  Hoppin  Hill  granitite  boss,  around  which  the 
horseshoe  fold  of  the  Wamsutta  is  l^ent. 

The  stratigraphic  position  of  the  block  can  be  only  vaguely  stated. 


RHODE  ISLAjS^D  COAL  MEASUEES. 


183 


In  succession  and  sediments  it  strongly  resembles  the  beds  which  appear 
in  East  Providence  and  Seekonk  in  the  middle  portion  of  the  coal-beai'ing 
series.  The  following  is  a  more  explicit  accomit  of  the  supposed  faults 
which  form  the  block  : 

Blake  Hill  thrust  plane. — If  a  line  be  drawu  parallel  with  the  Walpole  and 
Wrentham  Railroad  tracks  at  Plainville  Station  and  a  little  west  of  the 
roadbed,  it  will  follow  closely  the  boundary  between  the  nearly  horizontal 
strata  of  the  Blake  Hill  block  on  the  west  and  the  vertical  strata  of  the 
country  on  the  east  (see  PI.  XV),  at  the  extreme  western  end  of  the  Mans- 
field syncline.  Opposite  the  Plainville  Station  this  boundary  line  turns 
westward  in  the  form  of  a  small  loop,  inclosing  several  outcrops  of  the 
nearly  vertical  slaty  strata  which  extend  into  the  area  of  horizontal  beds  at 
the  base  of  the  Blake  Hill  block.  It  is  evident  from  an  inspection  of  the 
relations  of  these  two  sets  of  rocks,  so  sharply  contrasted  as  regards  attitude 
and  secondary  structures,  that  the  vertical  series  passes  westwardly  beneath 


w 

B/oA&  ///// 

E 

^-^  ^s^ 

^^ 

Fig.  26. — Geological  section  of  Plainville  Valley  and  thrust  plane. 

the  Blake  Hill  block.  Both  sets  of  strata  belong  to  the  Coal  Measures' 
but  the  evidence  from  fossils  so  far  found  is  not  sufficient  to  determine  the 
relative  position  in  the  normal  sequence  of  beds. 

The  Mansfield  syncline  is  overturned  between  North  Attleboro  and 
Shepardsville,  and  the  evidence  in  the  field  points  to  strong  pressure 
exerted  from  the  south  and  east  upon  this  region.  It  was  probably  a  result 
of  this  pressure  that  the  Blake  Hill  block  was  thrust  northward  upon  the 
edges  of  the  broken  Mansfield  syncline.  The  position  of  the  strata  in  the 
Blake  Hill  block  in  the  system  of  folds  before  these  were  broken  is  hope- 
lessly lost  in  the  diverse  structure  of  this  troubled  and  now  deeply  eroded 
area. 

Faults  occur  in  the  Blake  Hill  block  west  of  the  Plainville  thrust 
plane  and  parallel  with  its  outcrop.  They  are  developed  on  a  small  scale. 
These  faults  are  shown  by  two  classes  of  facts:  (1)  The  monoclinal  ridges 
of  hard  sandstone  and  quartzose  conglomerate  which  strike  northwest  are  in 


184  GEOLOGY  OF  THE  NAREAGANSETT  BASIN. 

line  with  offsets  in  the  Attleboro  sandstone  which  bounds  the  block  on  the 
south.  Goat  Rock  itself  is  the  highest  of  these  monoclinal  ridges.  (2)  An 
earlier  fault  has  brought  the  gray  Carboniferous  rocks  down  into  a  right- 
angled  contact  with  the  massive  Attleboro  sandstones.  West  of  the  Goat 
Rock  section  the  red  series  is  met  with  in  a  few  outcrops  and  in  a  well  on 
the  northwest.  There  is  reason  to  believe,  therefore,  that  a  fault  bounds 
this  block  on  the  west  so  as  to  bring  the  red  Wamsutta  rocks  up  to  the 
surface.     (See  fig.  16,  p.  157.) 

THE  DIGHTON   CONGLOMERATE   GROUP. 
Roxbury  conglomerate      Edward  Hitcbcock:  Final  Eepoit  on  Geology  of  Massachusetts,  1841,  p.  538. 

Reference  has  already  been  made  to  a  coarse  congiomerate  bed 
believed  to  form  the  upper  limit  of  the  Coal  Measures.  The  name  Dightou 
conglomerate  is  here  given  to  a  group  of  coarse  conglomerates,  with  alter- 
nations to  sandstone,  found  as  the  highest  members  of  the  Carboniferous  in 
Dighton,  Somerset,  and  Swansea,  in  Massachusetts.  The  coarsest  conglom- 
erate bed  is  at  the  base  of  the  formation.  The  rocks  are  better  shown  in 
Swansea  than  in  Dighton,  but  the  latter  place  being  better  known  and  more 
accessible  for  the  purpose  of  examining  these  rocks,  the  latter  name  has 
been  chosen.  A  few  areas  of  coarse  conglomerates  elsewhere  are  referred 
to  this  horizon. 

The  Dighton  conglomerate  group  attains  where  most  developed  a  thick- 
ness of  about  2,000  feet.  Its  Carboniferous  age  is  not  definitely  proved, 
but  it  is  assumed  on  the  following  grounds:  The  Dighton  conglomerate 
directly  overlies  the  Coal  Measures.  It  is  not  derived  from  the  erosion  of 
underlying  Carboniferous  beds,  but  it  contains  larger  pebbles  of  upper 
Cambrian  quartzites  than  are  known  elsewhere  in  this  field  lower  down  in 
the  Carboniferous  section.  It  difiFers  from  other  Carboniferous  conglomer- 
ates only  in  that  the  fragments,  being  of  larger  size,  demand  for  their  trans- 
portation more  vigorous  processes  than  those  previously  active.  The  beds 
participated  in  the  folding  which  closed  the  Carboniferous,  and  there  is  no 
known  unconformity  between  the  Dig'hton  conglomerate  and  the  subjacent 
strata.  A  typical  outcrop  of  the  coarse  quartzite  cong-lomerates  of  this 
Dighton  group  may  be  seen  in  the  crossroads  nearest  the  southwest  base 
of  Great  Meadow  Hill.  One  quartzite  pebble,  8  inches  long,  contains  the 
brachio]3ods  of  the  upper  Cambrian  fauna. 


DIGHTON  CONGLOMERATES.  185 

In  this  northern  part  of  the  basin  the  several  exposures  of  conglomerate 
referred  to  the  Dighton  group  lie  in  the  inner  or  upper  part  of  synclines. 
This  is  true  of  the  Great  Rock  area  in  Rehoboth,  whence  the  rocks  extend 
eastward  to  "Rocky  Woods,"  near  Taunton.  Another,  and  perhaps  the 
best  area,  is  that  of  the  Dighton  syncline,  extending  from  Dighton  into 
Swansea.  Another  well-defined  syncline  in  which  these  beds  are  found 
forms  Ides  Hill,  west  of  Attleboro  village.  The  coarse  conglomerates  at 
Purgatory  and  Paradise  rocks,  in  synclines  near  Newport,  resemble  the 
rocks  of  this  horizon. 

The  outcrops  of  coarse  conglomerates  at  Swansea  Factory  and  imme- 
diately west  appear  locally  to  strike  northwest  and  dip  north,  indicating 
either  that  the  great  syncline  is  overturned  southward  or  that  there  is  here  a 
local  folding  along  the  northern  side  of  the  major  synclinal  fold.  Outcrops 
are  too  few  to  verify  either  hypothesis,  but  the  high  inclination  of  the 
observed  strata  southward  below  the  Dighton  group  shows  that  the  beds  on 
this  northern  side  of  the  synclinal  axis  stand  at  much  higher  angles  than 
do  those  on  the  southern  side.  The  Great  Meadow  Hill  syncline  is  nearly 
symmetrical,  but  the  Attleboro  syncline  on  the  north  is  unsymmetrical, 
with  vertical  dips  on  the  south  side  of  the  axis. 

The  Dighton  conglomerate  is  composed  mainly  of  grayish  and  green- 
ish quartzite  pebbles  in  the  southern  areas;  toward  the  north,  as  in  the 
Attleboro  area,  it  is  equally  rich  in  granitic  pebbles.  The  amount  of 
quartzite  in  this  group  must  represent  several  hundred  feet  of  strata 
stripped  ofP  the  adjacent  country  in  Carboniferous  times.  Many  of  the 
pebbles  are  fossiliferous,  carrying  the  upper  Cambrian  fauna  already 
described.  The  pebbles  vary  in  size  from  a  fraction  of  an  inch  to  rounded 
waterworn  cobbles  a  foot  in  diameter.  The  reduction  to  spheroidal  shapes 
apparently  indicates  their  passage  through  the  surf'  line  on  a  beach.     (See 

PI.  xni.) 

In  many  sections  the  pebbles  are  packed  together  with  the  pellmell 
structure  of  glacial  till;  the  paste  is  often  earthy  and  ferruginous,  and 
when  slightly  attacked  by  weathering  allows  the  pebbles  to  roll  out;  in 
other  sections  pebbles  and  paste  are  thoroughly  cemented,  so  that  the  rock 
breaks  up  only  along  joints. 

Now  and  then  a  pebble  shows  a  joint  recess  where  the  rolling  action 
did   not  continue    long    enough  to    reduce  it  to  the    form    characteristic 


186  GEOLOGY  OF  THE  NARRAGANSETT  BASIN. 

of  wear  on  a  beach.  The  frequency  with  which  this  occurs  in  the  larger 
pebbles  suggests  that  when  submitted  to  the  action  of  the  waves  the  bits 
were  angular  joint  blocks,  such  as  quartzites  affoi-d  when  broken  out  of  a 
cliff.  (See  photograph  of  one  of  these  joint  niches  in  pebbles,  PI.  XIV.) 
Here  and  there  an  indented  pebble  may  be  seen. 

The  Dighton  group  of  conglomerates  being  the  highest  member  in 
this  basin,  the  areas  in  which  it  occurs  are,  owing  to  the  deep  erosion  of  the 
basin,  somewhat  removed  from  the  present  margin.  The  distance  is  gen- 
erally from  3  to  4  miles. 

The  topography  of  these  conglomerate  areas  is  bolder  and  more  rugged 
than  that  of  the  other  rocks  in  the  basin  outside  of  the  Wamsutta  series. 
The  formation  abounds  in  rounded,  bare,  rocky  knobs,  with  steep  vertical 
bluffs  facing  outward  from  the  sj^nclinal  axis  over  the  area  of  the  Seekonk 
sandstones,  again  overlooking  recesses  in  the  formation  itself  Long  rocky 
ridges  also  abound,  as  in  Dighton,  Taunton,  and  Attleboro,  now  generally 
given  over  to  woods  on  account  of  the  scarcity  and  infertility  of  the  soil 
and  the  general  unsuitableness  of  the  surface  to  agriculture. 

The  conglomerate  masses  attain  elevations  of  150  to  180  feet  above 
sea  level,  or  of  80  to  100  feet  above  the  surrounding  level.  In  Swansea 
the  conglomerate  ridges  rise  to  160  feet;  in  Dighton,  to  180;  and  in  Attle- 
boro, also  to  180.  Near  Taunton,  the  Rocky  Woods  attain  an  elevation  of 
160  feet.  This  level,  indicated  by  the  elevation  of  the  conglomerate  ridges, 
is  someAvhere  near  that  of  the  Jura-Cretaceous  peneplain  were  it  extended 
eastwardly  over  the  Carboniferous  area.  The  excavation  of  the  strata 
below  this  level  must  be  attributed  to  erosion  in  the  Tertiary  period. 

These  conglomerate  areas  contain  the  headwaters  of  numerous  brooks, 
but  several  of  the  larger  streams  in  the  southern  part  of  the  field  flow 
across  them,  evidently  from  original  courses  which  have  been  superposed 
on  these  hard  rocks. 

It  remains  to  be  determined  whether  there  is  an  unconformity  betwe  ^n 
the  Dighton  conglomerates  and  the  subjacent  Seekonk  group.  It  is  to  be 
expected  that  even  within  the  same  geological  period  such  discordances 
would  exist  where  currents  were  developed  strong  enough  to  urge  cobbles 
a  foot  or  more  in  diameter  out  over  an  alluvial  plain  like  that  formed  of  the 
Coal  Measures.  The  original  thickness  of  the  group  is  also  a  matter  for 
further  investigation.     Were  there  higher  Coal  Measures  in  this  area?  And 


COAL  MEASURES  OF  THE  DEDHAM  QUADRANGLE.  187 

did  Permian  or  later  strata  overlie  them  ?  There  is  a  chance  that  in  the 
center  of  some  one  of  these  synclinal  areas  higher  beds  than  have  here 
been  recognized  may  be  discovered.  It  is  indeed  possible  that  the  whole 
of  the  Dighton  series  is  of  Permian  age. 

The  contemporaneous  flora  and  famia  of  the  conglomerate  are  as  yet 
practically  unknown..  The  brachiopods  and  Avorm  burrows  reported  in  the 
quartzite  pebbles  belong  to  the  upper  Cambrian  famia.     (See  p.  109.) 

EXTElSrSIOlSr  of  the  coal  measures  north  AXD  EAST  OF  TAUjSTTON. 

Having  described  a  typical  area  of  the  Coal  Measures  and  the  over- 
lying conglomerates  in  a  part  of  the  basin  where  evidence  of  their  structui'al 
relations  can  be  had,  it  is  now  purposed  to  describe  the  eastern  extension  of 
these  rocks,  where  the  structure  is  less  well  understood.  For  convenience, 
the  order  of  presentation  which  is  suggested  by  the  mapping  of  this  portion 
of  the  field  in  sheets  of  the  atlas  folio  will  be  followed,  for  the  reason  that 
within  the  limits  of  these  maps,  comprising  the  Dedham,  Abington,  Middle- 
boro,  and  a  part  of  the  Taunton  quadi'angles,  the  exposures  of  strata  are  too 
few  in  number  and  extent  to  permit  any  systematic  account  of  the  stratig- 
raphy. These  rocks  have  been  described  with  more  fullness  than  their 
importance  apparently  deserves,  partly  for  the  reason  that  they  have  not 
been  heretofore  described,  and  partly  because  they  are  the  sole  indications 
of  the  under  geology  of  the  eastern  part  of  the  Carboniferous  field. 

DEDHAM    QUADRANGLE. 

The  Carboniferous  rocks  of  the  main  basin  cover  the  larger  part  of 
the  southern  third  of  this  quadrangle.  After  we  pass  southward  and 
geologically  above  the  rocks  immediately  along  the  border,  outcrops 
are  too  few  to  give  more  than  a  very  general  view  of  the  stratigraphy. 
The  Coal  Measures  are  present  in  Mansfield  and  West  Bridgewater,  and 
probably  underlie  the  intermediate  towns.  The  surface,  outside  of  the 
glacial  sand  plains,  is  strewn  with  flaggy  micaceous  and  feldspathic  sand- 
stones suggesting  arkoses,  winch  agree  in  character  with  some  of  the  out- 
crops. A  few  conglomerate  bowlders  of  the  gray  series  occur,  but  never  in 
the  abundance  which  characterizes  the  proximity  of  the  coarse  Dighton 
group  in  other  parts  of  the  field.  There  is  also  absent  the  hilly  and  rough- 
ened topography  which  accompanies  these  latter  beds  when  they  occur  in 


188  GEOLOGY  OF  THE  NAERAGANSETT  BASIN. 

synclinal  areas,  and  it  is  evident  that  these  upper  portions  of  the  Carbon- 
iferous have  disappeared  by  erosion  from  this  northern  field.  The  rela- 
tively gentle  dips  along  this  margin,  together  with  the  observed  great 
thickness  of  the  formation  where  fully  developed,  would  carry  the  outcrop 
of  the  uppermost  beds  several  miles  south  of  the  border  and  out  of  the 
Dedham  quadrangle. 

The  structure  of  the  strata  in  this  area,  so  far  as  it  can  be  made  out 
from  observed  outcrops,  is  mainly  synclinal.  The  axis  of  this  fold  passes 
approximately  through  Mansfield  Jtuiction  and  South  Easton;  or,  in  general 
terms,  lies  at  a  distance  of  from  2  to  3  miles  from  the  northern  border. 
The  trough  is  broad  and  shallow  toward  Brockton,  but  its  sides  steepen 
westward  toward  Mansfield,  and  between  North  Attleboro  and  the  border 
it  is  much  compressed,  and  the  folded  strata  are  finally  lost  to  view  beneath 
the  block  at  Blake  Hill.  Its  general  features  in  the  Mansfield  area  are 
shown  in  fig.  27,  on  p.  190.  The  following-  observations  set  forth  the  evidence 
in  typical  areas,  about  Mansfield  and  Bridgewater: 

MANSFIELD   AREA. 

There  are  no  surface  exposures  in  the  immediate  vicinity  of  the  West 
Mansfield  coal  mines,  the  rock  having  been  found  in  digging  a  well.  The 
lowest  strata  of  the  Carboniferous  appear  nearly  4  nules  north  of  the  coal 
mines,  dipping  gently  off"  to  the  south  from  the  hornblendic  granitite  of 
the  A¥rentham-Hingham  uplift.  The  basal  arkoses  and  grits,  described  with 
the  Wamsutta  series  (pp.  135-139),  form  conspicuous  ledges  on  the  southern 
face  of  Foolish  Hill,  in  Foxboro.  The  Wamsutta  series  has  here  a  possible 
thickness  of  1,000  feet.  It  is  succeeded  on  the  south  by  quartz  pebble 
and  quartzite  conglomerates  and  gray  sandstones,  forming  glaciated  ledges 
scarcely  above  the  general  surface  of  the  glacial  drift.  Southward  from 
Foolish  Hill  toward  Mansfield  Junction,  beds  of  sandstone  and  conglom- 
erates appear,  dipping  about  25°  S.  A  roche  moutonne'e  gives  the  follow- 
ing section  from  the  top: 

Section  of  a  roche  moutonne'e  in  the  Mansfield  area. 

reet.  In. 

6.  Saudstone,  with  layers  of  slate  pebble  cougloiuerate 6  6 

4.  Saudstone 3  6 

3.  Couglomerate,  with  slate  pebbles 1  0 

2.  Saudstone 5  0 

1.  Conalomerate,  base  not  seen 10  0 


COAL  MEASURES  OF  THE  DEDHAM  QUADRANGLE.     189 

These  beds  dip  to  the  S.  30° ;  the  cleavage  dips  N.  50°.  The  exposure 
is  noteworthy  in  exhibiting  preexisting  dark  slates,  broken  "up  and  deposited 
at  this  time.  The  slate  fragments  are  angular  and  conspicuous  elements  in 
the  layers  in  which  they  occur.  They  vary  in  length  from  3  to  4  inches 
and  in  thickness  from  1  to  2  inches.  The  attitude  of  the  fragments  and  the 
unruptured  state  of  the  stratum,  except  for  joints  and  cleavage,  preclude  the 
formation  of  the  slate  fragments  by  tire  disruption  in  post-Carboniferous 
times  of  an  original  argillaceous  layer.  For  similar  reasons,  the  fragments 
are  not  to  be  regarded  as  contemporaneous  pockets  of  argillaceous  sedi- 
ments. In  the  absence  of  contained  fossils  or  other  evidence  of  the  age 
of  these  pebbles,  there  is  doubt  whether  they  are  fragments  of  the 
subjacent  Carboniferous  shales  or  are  detached  pieces  of  the  dark  slates  of 
middle  Cambrian  age,  remnants  of  which  occur  at  Braintree,  in  the  Boston 
Basin.  The  not  infrequent  occurrence  of  signs  of  contemporaneous  erosion 
in  the  Cai-boniferous  beds  in  the  basin  leads  me  to  conclude  that  the  con- 
glomerates are  of  the  class  called  "  intraformational "  by  Walcott.^  I  have 
already  described  a  limited  occiu-rence  of  this  kind  at  the  contact  of  red 
and  gray  beds  in  Attleboro.  North  and  east  of  the  junction  at  Mansfield 
occur  a  few  outcrops  of  conglomerate  with  small  pebbles  and  associated 
sandstones.  At  the  junction  are  two  exposures  of  grayish  feldspathic  sand- 
stone— massive  beds,  like  the  typical  sandstone  ridges  of  the  Seekonk 
formation.  The  knob  west  of  the  railroad  carries  the  flattened  impression 
of  a  large  tree,  and  the  rock  in  the  railroad  cut  is  much  shattered. 

One  and  a  half  miles  south  of  the  Junction  is  a  locality  where  coal  was 
formerly  mined  (see  PI.  XVI).  In  the  absence  of  surface  exposures,  and 
because  of  the  abandonment  of  the  old  shafts,  it  is  impossible  to  get  other 
data  concerning  the  structure  at  this  locality  than  those  furnished  by  the 
records  of  earlier  surveys  and  by  one  recent  boring.  From  the  Massachu- 
setts report^  it  woidd  appear  that  the  beds  here  strike  NW.-SE.  and  dip 
NE.  from  30°  to  35°,  or  as  high  as  45°,  and  in  another  place  that  the 
strike  of  the  beds  is  NE.-SW.;  but  the  observation  of  C.  T.  Jackson,^  that 
the  "strata  between  which  the  coal  beds  are  included  run  quite  uniformly 

'C.D.Walcott:  Bull.  C4eol.  Soc.  Am.,  Vol.  V,  1894,  pp.  191-198;  Bull.  U.  S.  Geol.  Survey  No.  134, 
1896,  pp.  34-40. 

-  Final  Report  on  the  Geology  of  Massachusetts,  1841,  pp.  133,  540. 
3  Geology  of  Rhode  Island,  1840,  p.  107. 


190  GEOLOGY  OF  THE  ISTAREAGAKSETT  BASIN. 

ENE.-WSW.,  and  dip  to  the  NNW.  53°,"  is,  in  my  opinion,  approximately 
accurate. 

Both  C.  T.  Jackson  and  Edward  Hitchcock  agree  in  giving  a  northerly 
dip  to  the  rocks  at  this  point,  from  which  it  is  evident  that  the  Mansfield 
coal  beds  occur  on  the  south  flank  of  a  syncline,  and  may  be  expected  to 
reappear  on  the  northern  side  of  the  axis  or  in  the  vicinity  of  the  Junction. 
The  probabilities  are,  however,  that  the  sediments  in  this  direction  become 
coarser  as  the  shore  line  is  approached,  and  that  the  coal  beds  either  thin  or 
entirely  disappear.  The  coal  in  Foxboro  reported  by  Edward  Hitchcock, 
nevertheless,  may  be  a  reappearance  of  the  coal  on  the  northern  side  of 
the  axis. 

One  and  a  half  miles  south-southeast  from  West  Mansfield  Station,  in 
the  Taunton  quadrangle,  red  and  gray  sandy  slates  occur  with  nearly 
vertical  dips  striking  N.  64°  E.,  indicating,  along  with  other  outcrops 
described  in  connection  with  that  atlas  sheet,  the  much  steeper  southern 
side  of  tlie  syncline  and  the  passage  to  the  adjoining  anticline.  The  accom- 
panying section  (fig.  27)  represents  the  known  and  inferred  portions  of  the 
structure  through  the  Mansfield  area: 


Fig.  27.— Section  of  tlie  Mansfield  Coal  Measures.  The  lines  represent  obaerved  beds  and  their  underground  extension 
A,  Foolish  Hill  granititei  B,  "Wamsatta  series;  C,  Mansfield  Junction.  D,  West  Mansfield  mines.  E,  vertical  strata 
south-southeast  of  last. 

Analyses  of  two  coals  met  with  at  depths  of  about  90  and  850  feet, 
respectively,  in  a  boring  put  down  near  the  old  Hardon  mine,  have  been 


COAL  MEASUEES  OE  THE  DEDHAM  QUADRANGLE. 


191 


published  by  Dr.  A.  B.  Emmons.^     In  the  annexed  table,  analysis  No.  I  is 
from  the  90-foot  coal,  and  No.  II  from  the  8.50-foot  bed. 

Analyses  of  coals  front  the  Mansfield  area. 


Water 

Volatile  combustible  . 

Carbon 

Ash 


Sulphur 

Fuel  ratio  ( 


Carb.       \ 
Vol.  comb,  y 


1.02 

3.76 

74.24 

20.97 


99.99 

.56 


3.08 
6.22 
79.68 
11.02 


100. 00 


Thin  sections  from  the  core  made  in  this  boring,  according  to  a 
manuscript  report  b)^  Prof.  Collier  Cobb,  showed  that  the  amount  of  meta- 
morphisni  varies  Avith  the  depth,  being  greater  at  the  bottom  than  near  the 
surface. 

Flora  of  the  Mansfield  section. — TliB  followiiig  plauts  liave  becii  rcportod  from 
the  shales  at  Mansfield: 

Prof.  Edward  Hitchcock^  figured  forms  referable  to  the  genera — 


Pecojiteris. 

Sigillaria. 

Cordaites  (a  form  close  to  C.  robbii.) 


Calamites. 
Si^henopbyllum. 
Asteropliyllites. 
Auuularia. 

Leo  Lesquereux^  has  described: 

Sphenopteris  salisbnryi  (n.  s.). 
Ehacophyllum  adnasceus. 

Teschemacher*  described  and  named  several  forms,  some  of  which  are 
of  doubtful  identification: 


Pseudopecopteris  irregularis. 


Neuropteris  angustifolia. 
heterophylla. 
Pecopteris  loschii. 
borealis. 


Pecopteris  gigantea. 

Sphenophyllum  truncatum  (said  to  be  un- 
known except  to  Teschemacher). 
Sphenophyllum  dentatum=erasum. 


'Trans.  Am.  Inst.  Min.  Eng.,  Vol.  XIII,  1885,  p.  515. 

-  Final  Report  on  the  Geology  of  Massaohusets,  1841. 

'  Providence  Franklin  Society  Report  on  the  Geology  of  Rhode  Island,  1887. 

•'Boston  Jour.  Nat.  Hist.,  Vol.  V,  1846,  pp.  370-385. 


192  GEOLOGY  OF  THE  NABRAGANSETT  BASHST. 

BRIDGEWATEE   AREA. 

The  available  exposures  from  Brockton  soiitliward  through  the  Bridge- 
waters  indicate  a  broad  syncline  with  low  dips,  and  hence  a  much  more 
shallow  trough  than  that  near  Mansfield.  Southerly  dips  are  found  in  out 
crops  from  the  granitites  north  of  Brockton  for  a  mile  or  more  to  the  south 
of  that  city.  At  Cochesett,  and  thence  southward,  northerly  dips  are 
encountered  as  far  as  the  northern  part  of  the  Taunton  and  Middleboro 
quadrangles,  in  the  vicinity  of  Scotland,  about  3  miles  south  of  the  limits  of 
the  Dedham  quadrangle. 

Ovei'lying  the  chocolate-colored  sandstones  at  Brockton,  described 
tinder  the  head  of  the  Wamsutta  group,  occur  arenaceous  and  argillaceous 
strata  of  slaty  structure.  Exposures  of  a  bluish  coarse  sandstone  have 
been  made  in  opening  new  highways  northwest  of  Campello,  at  the  corner 
of  Adams  and  Center  streets.  One  and  a  half  miles  south-southeast  from 
this  locality,  on  the  west  side  of  Salisbury  Plain  River,  bluish-green  slates 
form  a  small  outcrop.  The  cleavage  is  E.-W.,  and  dips  45°  N.,  the  pre- 
vailing direction  and  steep  dip  along  the  northern  border.  Bowlders  of 
grayish  sandstone  occur  in  the  vicinity. 

Going  southward  across  the  strike,  the  next  exposure  is  in  the  railway 
cut  a  mile  east  of  Cochesett  Station.  The  strata  here  dip  from  5°  to  10° 
N.,  and  aiford  the  following  section  from  the  top  downward: 

Section  east  of  Cochesett  Station. 

reet. 

3.  Conglomerate ;  pebbles  of  quartzite  aud  smoky  quartz 10 

2.  Sandstone  and  arkose,  gray . 10 

1.  Sliale,  blue  and  comj^act 10 

A  thrust  plane,  with  slickensides  trending  N.-S  ,  was  noted  on  one  bed, 
and  there  are  to  be  seen  sn^iall  vertical  quartz  veins  containing  cavities  lined 
with  botryoidal  limonite. 

About  a  mile  south  of  the  Cochesett  exposure,  coal  is  represented  to 
have  been  found,  in  the  area  between  the  Hockamock  and  Town  brooks.^ 
The  place  of  this  bed  would  be  at  a  depth  of  about  1,800  feet  beneath  the 
Cochesett  section. 

1  Edward  Hitchcock:  Report,  1833,  p.  277;  Final  Report,  1841,  p.  129,  also  on  geological  map. 
C.  H.  Hitchcock :  Geological  map  in  Walling  and  Gray's  Atlas  of  Massachusetts,  1871. 


KHODE  ISLAND  GOAL  MEASURES.  193 

The  extension  along  their  sti-ikes  of  the  several  strata  thus  obscurely 
exposed  can  not  be  traced  with  certainty  more  than  a  few  rods.  As  in  the 
Mansfield  area,  there  are  no  indications  of  the  higher  beds  of  the  Carbonif- 
erous section,  so  well  exposed  in  the  deep  synclines  of  Dighton  and  Taun- 
ton. The  beds  for  the  most  part  appear  to  belong  to  the  few  hiuidred  feet 
of  Coal  Measures  coming  in  above  the  red  Wamsutta  series.  Unless  the 
Carboniferous  formation  thinned  out  in  this  direction,  the  post-Carbonifer- 
ous erosion  of  beds  of  this  age  alone  in  this  field  must  be  measured  as 
upward  of  10,000  feet  of  strata. 

ABINGTON  QUADRANGLE. 

In  the  southern  part  of  this  quadrangle  more  has  not  been  possible 
than  roughly  to  discriminate  the  lower  reddish  strata  of  the  Wamsutta 
extension  from  the  area  occupied  by  the  gray  Carboniferous  strata  of  the 
Coal  Measiu-es.  The  first-named  series  has  already  been  described  on 
page  143. 

There  are  about  a  dozen  exposures  of  the  gray  series  of  the  Coal 
Measures  known  in  this  quadrangle.  Beginning  on  the  northwest,  in 
Abington,  the  gray  series  is  seen  in  a  small  outcrop  about  1^  miles  south 
from  the  granitite  border.  It  is  over  5  miles  from  this  locality  southward  to 
the  outcrops  including  Sachems  Rock  near  the  Satucket  River,  in  the  town 
of  East  Bridgewater. 

Sachems  Rock  is  a  knob  about  175  feet  long  and  20  feet  high,  composed 
of  massive-bedded,  somewhat  altered  sandstone  with  bands  of  small  pebbles 
of  white  and  smoky  quartz,  a  fine-grained  granitic  rock,  and  a  slate  of 
undetermined  origin.  The  attitude  of  the  beds  is  nearly  horizontal,  dipping, 
if  at  all,  to  the  north.  There  is  a  pronounced  cleavage  striking  N.  77 °W. 
The  western  side  of  the  ledge  has  been  opened  for  the  jDurpose  of  quarry- 
ing-. The  smaller  exposures  to  the  east  along  the  street  are  like  the  first, 
showing  to  the  eye  abundant  miniite  scales  of  muscovite.  The  cleavage 
planes  maintain  the  same  direction,  and  dip  steeply  to  the  north. 

These  beds  are  on  the  southern  side  of  the  broad,  shallow  syncline 
which  covers  the  southern  part  of  the  Dedham  area,  next  north.  They 
would  come,  in  accordance  with  the  supposed  structure,  low  down  in  the 
Coal  Measures. 

In  Hanover,  half  a  mile  east  of  Drinkwater  River,  and  about  2,]  00 

MON  XXXIII 13 


194  GEOLOGY  OF  THE  iTAERAGANSETT  BASIK 

feet  soutli  of  tlie  northern  border,  is  a  probable  outcrop  of  gray  Carbonifer- 
ous sandstone  in  tlie  street;  it  may  be  a  large  bowlder.  Bowlders  of  the 
same  lithological  texture  are  abundant  upon  the  surface.  Southward  to 
the  limits  of  the  quadrangle  no  outcrops  have  been  found. 

Eastward,  in  tlie  vicinity  of  Hanover  Four  Corners  and  near  the  east- 
ern igneous  border,  several  outcrops  of  the  carbonaceous  series  appear. 
Beginning  on  the  northeast,  in  South  Scituate  on  the  east  bank  of  Third 
Hemng  Brook  there  is  either  a  large  bowlder  or  an  outcrop  of  sandstone 
with  bands  of  small  pebbles.  Southward,  where  the  road  from  Hanover 
Four  Corners  to  North  Pembroke  crosses  North  River,  there  are  good 
exposures,  forming  a  narrow  defile  through  which  the  river  escapes  from  a 
broad  valley  on  the  west  to  the  wide  channel  extending  beyond  this  cut 
to  the  sea.  The  strata  are  sandstone  and  arkose  with  coarse  grits,  bands 
of  slate,  and  carbonaceous  matter,  striking  in  an  east-west  direction  and 
standing  at  high  angles.  On  the  soutli  side  of  the  river,  in  August,  1889, 
there  was  found  in  a  coalj^  seam  the  stem  of  a  calamite. 

One  and  a  half  miles  farther  up  the  North  River,  where  it  is  crossed 
by  the  west  road  from  the  Corners  to  Pembroke,  other  exposures  of  the 
Carboniferous  conglomerates  and  sandstones  occur,  on  the  south  side  of  the 
stream.  At  the  edge  of  the  stream,  in  July,  1889,  conglomerates  and 
sandstones  were  exposed  under  a  mill.  The  bedding  was  much  obscured 
by  joints.  A  few  rods  southward  a  blue  compact  sandstone  is  exposed,  by 
the  roadside,  apparently  overlying  the  above-named  beds.  Across  the  road 
and  a  few  yards  south  of  this  cut  a  well  was  sunk,  in  July,  1889,  through 
10  feet  of  till  into  a  dike  of  fine-grained,  dark-colored  diabase  containing 
numerous  inclusions  of  granitic  quartz  from  one-eighth  to  one-half  inch 
across,  and  a  few  pieces  of  feldspar.  Angular  fragments  of  red  granitite 
also  occur  in  the  diabase. 

Half  a  mile  farther  up  the  river  the  stream  lays  bare  a  section  of 
closely  jointed  sandstones  apparently  dipping  northward.  In  the  bank 
above  the  carriage  road  there  is  much  carbonaceous  waste.  In  the  road 
ascending  the  hill  at  the  head  of  the  westernmost  of  the  thi-ee  headwater 
branches  of  Swamp  Brook,  in  Pembroke,  black  clays  occur,  which  are  also 
met  with  in  excavations  on  the  adjoining  laud.  The  relations  of  these 
deposits  are  very  uncertain. 


EHODE  ISLAND  COAL  MEASURES.  195 

TAUNTON   QUADRANGLE. 

The  eastern  part  of  the  area  designated  the  Taunton  quadrangle  is 
nearly  devoid  of  outcrops.  In  general  it  may  be  said  that,  except  for  a 
triangular  area  on  the  southeast  equal  to  about  one-ninth  of  the  whole,  this 
quadrangle  is  occupied  by  the  rocks  of  the  Carboniferous  system.  The  strata 
which,  appear  at  the  surface  are  mainly  the  harder  conglomerates  and  sand- 
stones, thrown  into  anticlines  and  synclines.  Of  these  structures  there  are 
at  least  two  well-defined  sets  in  the  western  part  of  the  quadi-angle:  the 
Dighton  syncline,  with  coarse  conglomerates,  coming  to  a  nose-like  end  at 
Dighton  in  Richmond  Hill;  and  the  Great  Meadow  Hill  or  Taunton  syn- 
cline, with  the  coarse  conglomerates  of  the  "Rocky  Woods,"  west  of 
Taunton.  Between  these  two  great  conglomerate  areas  lies  the  axis  of  an 
anticline  which  probably  traverses  the  area  eastward  to  Middleboro.  On 
the  northern  side  of  the  Rocky  Woods  tract  is  an  anticlinal  axis  with  nearly 
vertical  strata,  north  of  which  lies  the  Mansfield  syncline. 

The  deposits  so  far  recognized  range  from  the  highest  beds  in  the  for- 
mation, including  the  Dighton  conglomerates,  downward  toward  the  middle 
of  the  Coal  Measures  section,  including  members  of  the  Seekonk  and  Ten- 
mile  River  beds.  The  precise  position  of  the  lowest  strata  seen  is  not  defi- 
nitely known.  The  following  notes  pertain  to  important  natural  exposm-es 
of  the  strata  and  to  artificial  openings. 

Red  beds. — At  one  point  in  the  northwestern  part  of  the  quadi-angle,  about 
1^  miles  southeast  of  West  Mansfield  Station,  in  the  road  on  the  west  side  of 
Hodges  Brook,  red  slates  are  in  contact  with  gray  beds,  striking  N.  64°  E., 
with  nearly  vertical  dips.  This  is  the  only  exposure  of  red  beds  known 
in  this  area,  but  whether  they  are  an  extension  of  the  red  slates  in  Attle- 
boro  or  are  a  reappearance  of  the  Wamsutta  group,  there  is  no  means  of 
deciding.  The  red  slates  in  the  drift  south  of  this  point  afford  plainly 
marked  flattened  impressions  of  calamites. 

Outcrops  in  Norton. — Midway  betwceu  Norton  village  and  the  southwestern 
arm  of  the  Norton  reservoir  is  a  low  outcrop  exposing  about  100  feet  of 
conglomerates,  sandstones,  and  slates.  The  strike  here  is  nearly  NE.-SW. 
The  conglomerate  is  composed  of  quartz,  quartzite,  and  granitic  pebbles 
varying  from  half  an  inch  to  3  or  4  inches  in  diameter.  These  beds  can 
be  traced  eastward  for  a  quarter  of  a  mile.     Unless  they  are  overturned 


1  96  GEOLOGY  OF  THE  NARRAGANSETT  BASIX. 

tliey  overlie  the  following  section,  which  is  separated  from  them  by  several 
hmidred  feet  of  concealed  beds. 

Near  the  southeastern  end  of  the  Norton  reservoir  are  broad  exposures 
of  slaty  arenaceous  strata  striking  N.  54°  E.  and  dipping  75°  S.  The  fol- 
lowing paced  measurements  give  the  succession,  from  south  to  north: 

Section  in  Norton. 

Feet. 

1.  Slate 3 

2.  Sandstone 39 

3.  Slate 5 

4.  Sandstone    2 

5.  Slate 12 

6.  Sandstone 8 

7.  Slate 1 

8.  Sandstone 27 

9.  Slate 9 

10.  Sandstone 18 

11.  Slate 48 

12.  Sandstone 22 

13.  Slate 2 

14.  Sandstone 34 

The  prevailing  character  of  this  section  is  similar  to  that  of  the  beds 
in  the  same  anticlinal  fold  to  the  westward  in  Attleboro.  The  absence  of 
carbonaceous  matter  in  the  exposed  sections  is  noteworthy. 

A  few  isolated  outcrops  in  the  village  of  Norton  display  beds  of  con- 
glomerate and  grits,  with  variable  dips.  At  one  point  the  inclination  is  as 
low  as  50°  N.  The  general  structure  of  the  belt  of  rocks  through  Norton 
is  probably  anticlinal,  for  the  Mansfield  and  Bridgewater  synclinal  trough 
lies  on  the  north  and  the  Grreat  Meadow  Hill  syncline  is  well  marked  on 
the  south. 

winneconnet  ledges. — Froui  2  to  3  mllcs  uortheast  of  the  exposures  in 
Norton  occurs  the  Winneconnet  section,  on  the  east  bank  of  Mulberry 
Meadow  Brook.  There  are  here  exposed  upward  of  200  feet  of  soft  slaty 
rock  of  an  areiiaceoxis  and  often  gritty  texture.  The  cleavage  dips  west, 
and  its  strike  is  N.  49°  E.,  but  the  dip  of  the  bedding  is  not  easily  deter- 
mined. One  and  a  half  miles  northwest  of  this  locality  is  another  exposure 
of  similar  slates.  In  both  places  the  surface  of  the  rock  weathers  into 
pear-shaped  and  rounded  cavities,  recalling  the  weathei'ing  of  the  ottrelitic 


RHODE  ISLA:N^D  GOAL  MEASURES.  197 

schists  along  the  shores  of  Narragansett  Bay.  It  is  probable  that  the 
metamorphism  of  the  beds  along  this  anticlinal  line  has  been  greater  than 
elsewhere  in  the  eastern  part  of  the  basin,  or  that  lower  beds  are  here 
exposed.     (See  fig.  6,  p.  120,  locality  B.) 

Eastward,  outcrops  appear  in  the  vicinity  of  Scotland.  About  three- 
fourths  of  a  mile  south  of  the  town  pebbly  sandstones  strike  nearly  E.-W. 
and  dip  about  20°  N.,  forming  a  low^  monoclinal  ridge  with  an  escarpment 
facing  the  south. 

Beginning  the  description  on  the  western  border  of  the  quadrangle 
again,  the  beds  on  the  south  side  of  this  broad  anticline  are  represented  by 
a  few  exposures.  The  best  of  these  is  at  a  point  near  the  western  margin, 
on  the  west  side  of  Chartley  Brook,  about  2  miles  south  of  the  Attleboro 
branch  of  the  Old  Colony  Railroad.  An  old  quarry  here  occui-s  in  a  knob 
of  the  gray  Carboniferous.  The  strike  is  N.  69°  E.,  the  dip  16°  S.,  and 
the  following  section  is  exposed  from  the  top  downward: 

Section  in  Chartley  quarry. 

Feet. 

Gray  sandstone  with  small  bauds  of  pebbles  and  flattened  stems  of  plants,  afford- 
ing traces  of  coal 20 

Black,  compact,  argillaceous  beds,  slightly  micaceous,  containing  worm  burrows  of 
a  scolithoid  habit;  exposed 12 

scoiithus  beds. — The  worm  burrows  referable  to  Scolithus  at  this  locality 
are  somewhat  sinuous  or  often  recurved  burrow^s  filled  with  material  similar 
to  the  micaceous  rock  of  the  walls.  The  tubes  vary  from  an  inch  to  a 
quarter  of  an  inch  in  diameter.  Where  the  wall  has  broken  away  from  the 
internal  cast  the  surface  is  either  smooth  or  rarely  marked  by  minute  cross 
striations.  The  tubes  are  closely  set,  sonietimes  apparently  in  contact. 
The  depth  of  the  burrow  exceeds  in  most  cases  2  inches,  and  is  probably 
much  deeper,  but,  on  account  of  the  interlacing  of  the  tubes,  this  point  can 
not  easily  be  ascertained.  There  seems  no  sufficient  reason  for  giving  a 
specific  name  to  these  forms,  since  they  have  no  importance  in  indicating 
horizons  even  within  the  limits  of  this  small  basin. 

One  and  a  half  miles  east  by  north  of  this  locality  are  outcrops  of 
compact  argillite,  succeeded  on  the  south,  near  the  head  of  Goose  Brook, 
by  gritty  sandstones  containing  distinct  pebble  bands,  the  dip  of  the  last 
being  as  steep  as  80°  S.     These  beds  appear  to  be  near  the  axial  line  of  the 


198  GEOLOGY  OP  THE  NAERAGAifSETT  BASm. 

anticline  which  is  traceable  westward  along-  the  valley  of  Tenmile  River 
in  the  Providence  quadrangle. 

Eastwardly  there  are  no  exposures  along  this  strike  line  until  we  reach 
the  small  quarry  of  gray  sandstones  opened  alongside  the  railroad  between 
Britanniaville  and  the  junction  of  the  Attleboro  branch  railroad.  About 
li  miles  north-northeast  outcrops  occur  on  the  west  of  Scudding  Pond. 
About  4J  miles  farther  east  coal  has  been  reported  on  the  southern  border 
of  Gushee  Pond,  but  the  stratigraphy  of  this  region  is  concealed  by  di'ift. 

South  of  this  belt,  in  the  latitude  of  Taunton,  the  Seekonk  beds,  over- 
lying the  above,  come  in  with  southerly  dips  and  disappear  on  the  west 
beneath  the  sjmchnal  axis  on  which  stands  Great  Meadow  Hill.  The  strata 
are  medium  conglomerates,  sandstones,  and  shales.  Coal  has  been  found 
in  the  uppermost  beds  underlying  the  coarse  Dighton  conglomerates  about 
1-^  miles  northeast  of  Great  Meadow  Hill.  So  far  as  has  been  determined, 
this  is  the  highest  occurrence  of  coal  in  the  basin. 

Taunton  waterworks  section. — Eastwardly  aud  at  a  somewliat  lower  level,  though 
probably  in  the  horizon  of  the  Seekonk  beds,  coal  was  again  met  with  in 
sinking  an  artesian  well  for  the  waterworks  of  the  city  of  Taunton.  The 
well  penetrated  to  a  depth  of  975  feet.  The  dip  is  reported  to  have  been 
about  40°  N.  The  following  table  gives  the  thickness  of  the  several  strata 
penetrated.  The  data  were  furnished  by  Mr.  George  F.  Chace\  The 
measurements  are  approximate,  and  are  based  upon  the  nature  of  the 
materials  brought  up  by  the  sand  pump.  The  amounts  indicate  the  depth 
of  each  bed. 

Record  of  artesian-ivell  boring  at  Taunton. 

Feet. 

Superficial  deposits  (glacial  drift) 85 

Saudstoue 95 

Coaly  shales 20 

Slate,  blue 85 

Sandstone 20 

Conglomerate,  quartzose 12 

Sandstone 30 

Slate,  blue 81 

Sandstone 22 

Slate,  blue 80 

'Fourteenth  Annual  Report  of  the  Water  Commissioners  of  the  City  of  Taunton  [for  1889]. 
Taunton,  1890.     Plate  opposite  p.  28. 


EHODE  ISLAND  COAL  MEASURES. 


199 


Becord  of  m'tesian-well  boring  at  Taunton — Continued. 

Feet. 

Sautlstone  and  coaly  slate 

1  '\ 
Conglomerate,  quartzose 

Q7 
Coaly  shales 

Slate,  coaly,  and  sandstone 1^ 

5 

'    '        13 

7 


Sandstone.. 
Coaly  slate . 
Sandstone. 


Slate,  blue ^^ 

Coaly  slate . 
Slate,  blue . 
Coaly  slate 
Slate,  blue . 
Coaly  slate 
Slate,  blue . 


10 
5 
5 
10 
15 
3.3 


40 


Sandstone '^ ' 

Coaly  shale - ■ 

Sandstone -"^ 

975 


Depth  of  well 


Tlie  dip  of  the  strata  being,  as  stated,  about  40°  N.,  the  actual  thick 
ness  of  the  strata  passed  through  woukl  therefore  amount  to  639.6  feet. 

westviiie  section. — A  partial  section  of  these  rocks  occurs  on  the  west  bank 
of  Threemile  River  from  Westviiie  northward.      The   greater  portion   of 


Fig.  28.— Geological  section  in  Westviiie,  Massachusetts,  1  mile  west  of  Taunton.  5,  coarse  componnd  conglomerate, 
pebbles  often  a  foot  in  diameter  (Dighton  group) ;  4,  covered  space,  probably  sandstones ;  3,  fine  conglomerate,  quartzose 
pebbles;  2,  covered  space,  probably  shales;  1,  micaceous  flaggy  sandstones,  much  cleaved,  and  bearing  casts  and 
impressions  of  calamites. 

the  section  is  drift  covered,  but  enough  is  exposed  to  show  the  character  of 
these  upper  beds. 

A  similar  section  is  repeated  in  most  features  1  mile  east  of  Taunton, 
along  the  road  from  Taunton  to  East  Taunton. 

Westward  along  the  Providence  and  Taunton  turnpike,  2  miles  east 
of  Great  Meadow  Hill,  the  sandstones  and  fine  conglomerates  underlying  the 


200  GEOLOGY  OF  THE  NAREAGANSETT  BASIN. 

coarse  conglomerates  of  the  great  syncline  again  appear  in  good  exposures. 
Annawon  Rock  (if  it  is  not  a  bowlder)  and  the  conglomerates,  certainly  in 
place  at  this  locality,  come  a  little  lower  in  this  section. 

Southward  tliere  are  numerous  outcrops  of  sandstone  and  conglomerate, 
tintil  at  Swansea  Factory  the  northern  edge  of  the  Dighton  conglomerate 
in  the  type  syncline  again  comes  in.  The  thick  coating  of  di'ift  makes  a 
correlation  with  the  corresponding  outcrops  on  the  two  sides  of  the  anticline 
which  passes  northeasterly  across  this  field  well-nigh  impossible.  East- 
ward in  J3ighton  fine  conglomerates  come  in  below  the  coarse  beds  along 
Muddy  Cove  Brook.  Similar  conglomerates  crop  out  east  of  the  Taunton 
River,  and  again  south  of  the  syncline  in  Somerset. 

The  area  southward  to  the  Taunton  River  is  occupied  by  sandstones 
and  shales,  the  latter  appearing  along  the  river  shore. 

Taunton  River  Valley. — As  a  marked  cxcoption  to  the  easterly  strikes  of  the 
beds  in  this  field,  an  outcrop  just  east  of  Judson  post-office,  on  the  eastern 
margin  of  the  Taunton  quadrangle,  exhibits  a  north-south  strike.  This 
outcrop  marks  the  turn  of  the  strata  around  the  eastern  end  of  the  Taunton 
syncline.  The  ridge,  it  is  also  worthj^  of  note,  is  parallel  to  the  course  of 
the  Taunton  River  in  this  section. 

The  Taunton  River  exhibits  a  marked  adjustment  to  the  stratigraphy 
of  this  portion  of  the  field,  although  it  is  heavily  masked  by  glacial  drift. 
The  section  of  the  river  from  Taunton  eastward  is  along  the  strike  of  the 
soft  beds  and  across  the  strike  of  the  hard  beds.  It  is  for  this  reason  that 
its  east-west  reaches  are  long,  its  north-south  courses  short.  South  of 
Taunton  the  same  adjustment  is  less  perfectly  exhibited.  These  facts 
indicate  a  well-excavated  preglacial  channel. 

MIDDLEBORO    QUADRANGLE. 

But  few  outcrops  of  the  Carboniferous  are  exposed  within  the  limits  of 
the  Middleboro  quadrangle,  and  it  has  not  been  possible  to  do  more  than  to 
indicate  on  the  map  the  area  occupied  by  the  Carboniferous  formation  in 
general  without  reference  to  horizons.  The  information  gleaned  from 
bowlders,  while  it  does  not  permit  the  delineation  of  the  exact  distribution 
of  strata,  shows  that  this  portion  of  the  field  is  traversed  by  beds  of  con- 
glomerate, sandstone,  and  slate  resembling  those  of  the  Coal  Measures, 
and  probably  representing  the  lower  portion  of  that  series. 


EHODE  ISLAND  COAL  MEASURES.  201 

South  of  Middleboro,  on  the  west  bank  of  the  Namasket  River,  are 
thi'ee  low  outcrops  of  gritty  slate  with  thin  layers  of  white  quartz  pebbles, 
the  size  of  the  pebbles  being  not  over  an  inch  in  diameter.  Beds  of  this 
character  are  probably  not  far  above  the  base.  It  is  interesting  to  note 
again  in  connection  with  these  beds  the  outcrop  of  granitite  which  occurs 
immediately  north  in  Namasket  village. 

At  the  southwestern  border  of  Great  Cedar  Swamp,  although  there 
are  no  outcrops,  the  abundance  of  slabby  sandstones  in  the  fences  indicates 
the  probable  eastward  extension  of  the  sandstones  which  occur  near  the 
middle  of  the  Coal  Measures  in  the  western  part  of  the  basin. 

The  area  of  felsites  in  Plympton  has  already  been  described  (see 
p.  116). 


CHAPTER   VI. 

ORGANIC  GEOLOGY. 

In  1840,  Dr.  C.  T.  Jacksou  stated,  as  a  result  of  his  survey  of  the  Coal 
Measures  in  Ehode  Island,  that,  "from  the  fossil  contents  of  the  Carbonifer- 
ous clay  slate,  we  have  reason  to  regard  it  as  a  fresh-water  deposit,  either 
from  lakes  or  from  the  estuary  of  some  ancient  river,  whose  waters  may 
have  brought  down  from  the  lowlands  on  its  banks  an  abundance  of  these 
specimens  of  the  ancient  flora."  ^  No  observations  of  more  recent  date  have 
been  published  to  overthrow  Jackson's  hypothesis  of  the  uoumarine  origin 
of  the  sediments  now  preserved  in  the  basin.  Knowledge  regarding  the 
fauna  and  flora  has  been  gained  slowly,  and  mainly  through  the  work  of  a 
few  students  resident  in  the  Rhode  Island  part  of  the  field. 

Besides  insects,  the  Pawtucket  shales,  according  to  Prof.  A.  S.  Pack- 
ard,^ have  afforded  "the  impression  of  an  annelid  worm,  several  shells  of 
Spirorbis,  and  what  appears  to  be  the  track  of  a  gastropod  mollusk." 

IlSrSECT  FAUNA. 

Mr.  Samuel  H.  Scudder  has  described  and  figured  a  small  insect  fauna 
collected  by  various  persons  in  the  shales  about  the  head  of  Narragansett 
Bay.  The  following  list  is  compiled  from  his  paper.  Insect  Fauna  of  the 
Rhode  Island  Coal  Field  :^ 

Insect  Jawna  about  the  head  of  Narragansett  Bay. 


Kame. 

Based  upon — 

Locality. 

Araclinida  (spiders) : 

Pawtucket,  R.  I. 

Neuropteroidea : 

(Not  extant). 

ton,  R.  I. 

Orthopteroidea : 

PalfeoblattarifB — 

MylacridiB — 

Mylacris  packardii 

AVing 

Bristol  and  Pawtucket,  R.  I. 

•Report  on  the  Geology  and  Agriculture  of  Rhode  Island,  pp.  37-38. 
-iAm.  Jour.  Sci.,  3il  series.  Vol.  XXXVII,  1889,  p.  411. 
3  Bull.  U.  S.  Geol.  Survey  No.  101,  1893,  27  pp.,  2  pis. 


POSITION  OF  THE  INSECT  FAUNA. 

Insect  fauna  ahoiii  the  head  of  Narragansett  Bay — Continued. 


203 


Name. 

Based  upon—                                   Locality. 

Orthopteroidea — Continued : 
Blattinari;e  (cockroaches) — 

Pawtucket?  E.I. 

Silver  Spring,  E.  I. 

Pawtucket,  E.  I. 

E.  Providence,  E.  I. 

Cranston,  E.  I. 

Pawtucket,  E.  I. 

E.  Providence,  E.  I.  (Drift.) 

Pawtucket,  E.  I. 

Pawtucket,  E.  I. 

Silver  Spring,  E.  I. 

Silver  Spring,  E.  I. 

SP 

Fore  wing 

Fore  wing 

Hind  wing 

gorhami 

Fore  wing 

Protophasmida  (leaf  and  stick  insects) : 

STRATIGRAPHIC  POSITION   OF  THE  FAUNA. 

The  discoverers  of  this  interesting  insect  fauna  appear  to  have  done 
little  toward  establishing  the  horizon  or  horizons  in  whicli  it  occurs,  if  it 
has  any  assignable  limits.  The  specimen  of  Etoblattina  from  Fenner's 
ledge  in  Cranston,  so  Mr.  Scudder  quotes,  was  found  "near  the  extreme 
western  upturned  edge  of  the  Carboniferous  in  the  plumbago  mining  district, 
and  [is]  therefore  probably  older  than  the  others."  ^ 

The  localities  which  have  so  far  furnished  these  insect  remains  are 
traversed  by  strata  relatively  low  down  in  the  Coal  Measures  section. 
The  outcrops  in  East  Providence  are  in  the  horizon  of  the  Tenmile 
River  beds.  The  shales  of  the  Cranston  series  lying  to  the  west  of  these 
exposures  are  probably  in  part  still  lower  in  the  section,  extending  down- 
ward nearly  to  the  base  of  the  Carboniferous.  It  would  appear,  therefore, 
that,  so  far  as  at  present  known,  this  fauna  ranges  from  near  the  base  of 
the  Coal  Measures  to  and  into  the  Tenmile  River  beds.  The  higher  strata, 
which  have  a  nearly  equal  thickness,  have  not  afforded  fossils.  The  locality 
at  Bristol  is  somewhat  in  doubt  as  to  its  place  in  the  section. 

ODONTOPTERIS    FliORA. 

The  flora  of  the  Rhode  Island  Coal  Measures,  according  to  the  list  of 
plants  collected  by  the  Rev.  E.  F.  Clark  and  identified  by  the  late  Leo 

'Op.  cit.,  p.  IG. 


204 


GEOLOGY  OF  THE  NAERAGANSETT  BASIN. 


Lesquereux,  is  peculiarly  rich  in  species  of  Odontopteris.  As  yet  the  upper 
portion  of  the  Coal  Measures,  from  near  the  base  of  the  Dighton  group 
upward  in  the  northern  field,  has  afforded  little  or  no  evidence.  From  the 
list  of  localities  which  appear  to  have  been  visited  in  collecting  the  fossils 
in  Lesquereux's  list  it  is  possible  to  draw  conclusions  of  some  value  regard- 
ing the  flora  so  far  as  it  is  known. 

The  localities,  so  far  as  the  Providence  quadrangle  is  concerned,  are 
practically  limited  to  the  exposures  which  occur  in  the  lower  half  of  the 
series  of  sandstones  and  shales  of  the  Coal  Measures,  or  to  essentially  the 
same  range  as  the  insect  fauna.  Lesquereux^  concluded  from  these  plants 
that  the  Rhode  Island  Coal  Measures  were  equivalent  to  the  beds  of  the 
upper  Carboniferous  in  Pennsylvania.  Until  the  flora  of  the  uppermost 
members  of  the  period  in  this  basin  is  known  nothing  further  can  be  said 
regarding  their  Permian  affinities.     (See  also  pp.  170,  181,) 

List  of  plants  identified  hy  Leo  Lesquereux.- 


Species 

Locality. 

Pawtucket. 

Valley  Falls. 

Pawtucket. 

Pawtncket. 

Pawtucket. 

Pawtucket. 

Pawtucket. 

Pawtucket. 

Valley  Falls. 

Valley  Falls. 

Valley  Falls. 

Pawtucket. 

Pawtucket. 

Pawtucket. 

Pawtucket. 

Pawtucket. 

Pawtucket. 

Pawtucket. 

Pawtucket. 

Pawtucket. 

Pawtucket. 

Bristol. 

Pawtucket. 

Pawtucket. 
Pawtncket. 

? 

9.  Neuropteris  deoipiens 

10.  Goniopteris  (Pecopteris)  unita 

14.  Sckizopteris  (Rhacophyllum)  trichomanoidos 

15.  Oligocarpia  gutbieri 

19.                       niiltoni  (same  as  13) 

22.  Pseudopecopteris  diuiorpha 

24.  Parallel  narrow  rachises  of  piunie  of  No.  7,  mostlj' 

!Am.  Jour.  Sci.,  3d  series,  Vol.  XXXVII,  1889,  p.  411. 
=  Ibid.,  p.  229. 


OCCURRENCES  OF  COAL.  205 

A  more  complete  list  of  plants  found  in  the  Rliode  Island  Coal  Meas- 
ures has  been  compiled  by  the  Franklin  Society  of  Providence,  and 
published  in  its  Report  on  the  Geology  of  Rhode  Island,  1887. 

COAL  BEDS. 

The  following-  account  of  the  coal  beds  in  the  basin,  written  by  Edward 
Hitchcock,  who  descended  into  all  the  accessible  mines,  sets  forth  the 
condition  of  things  as  late  as  1853,  since  which  time  few  mines  have  been 
opened: 

1.  Beds  of  coal  in  Mansfield. — These  have  been  opened  iu  two  parts  of  the  town. 
One  is  near  the  center,  where  a  shaft  was  sunk  by  the  Mansfield  Coal  Company,  some 
fifteen  years  ago,  64  feet,  but  only  a  little  coal  was  found. 

About  the  same  time  the  Mansfield  Mining  Company  sunk  a  shaft  84  feet  near 
the  Hardon  farm,  2  miles  southwest  of  the  center.  A  drift  was  then  carried  across 
the  strata,  and  it  is  said  that  seven  beds,  of  various  thickness  up  to  10  feet,  were 
found.     Dip  of  these  beds,  53°  NW.     Strike,  SW.  and  NE. 

More  recently,  in  1848,  I  believe,  the  Mansfield  Coal  and  Mining  Company, 
through  the  enterprise  and  perseverance  of  B.  F.  Sawyer,  esq.,  sunk  a  shaft  near  the 
same  place,  170  feet  and  10  feet  in  diameter,  from  which,  according  to  the  statements 
of  Thomas  S.  Eidgway,  esq.,  the  engineer,  they  have  carried  a  south  tunnel  6C0  feet, 
aud  other  tunnels  and  gangways  to  about  the  same  amount.  Not  less  than  thirteen 
beds  of  coal  have  been  crossed,  but  none  of  them  thick.  They  are  very  irregular, 
sometimes  swelling  out  to  6  or  8  feet  in  thickness,  and  then  pinched  up  to  a  few  inches. 
The  dip  varies  from  30°  to  70°  NW.,  and  the  strike  is  nearly  NE.  and  SW.  Although 
these  excavations  are  not  far  from  the  old  Hardon  mine,  the  beds  are  said  to  have 
little  correspondence. 

2.  Bed  in  Foxiorough. — This  is  only  about  2  miles  from  the  Mansfield  beds,  and 
two  excavations  were  made  there  several  years  ago,  and  good  coal  obtained,  but  the 
pits  were  filled  up  so  that  I  could  not  ascertain  the  strike,  dip,  aud  width  of  the  bed. 

3.  Beds  in  Wrentham. — In  the  south  part  of  the  town  a  i)it  was  sunk  many  years 
ago,  about  170  feet,  mostly  in  dark  carbonaceous  slate,  aud  several  beds  found.  The 
coal  which  I  have  seen  from  this  spot  is  not  good,  having  40  per  cent  of  ash.  Strike 
of  the  bed,  nearly  E.  and  W. ;  dip,  45°  N. 

i.  In  Baynham. — An  outcro])  of  coal  appears  in  this  town,  about  3  feet  thick, 
which  has  not  been  explored,  except  a  few  feet.     Strike,  N.  50°  E.;  dip,  45°  SE. 

5.  In  Bridgeicater. — Indications  of  coal  were  shown  me  from  the  rock  thrown  up 
in  digging  a  well  in  the  south  part  of  the  town,  but  nothing  further  could  be  learned. 

6.  In  Taunton. — Two  miles  northwest  of  the  town,  a  similar  opening  was  shown 
me,  but  I  could  not  learn  the  dip  and  direction  of  the  slate.  Four  miles  to  the  west 
of  the  town,  I  was  told,  similar  indications  exist.  The  same  is  true  of  West  Bridge- 
water,  and  in  Berkeley  coal  plants  are  found,  such  as  usually  accompany  beds  of 
coal. 


206  GEOLOGY  OF  THE  NAEEAGANSETT  BASIN. 

7.  In  Gumberland,  Rhode  Island. — This  is  called  the  Roger  Williams  miue,  whicli 
was  opened  many  years  ago;  but  the  works  were  burnt,  and  the  explorations  aban- 
doned, but  they  have  been  resumed  within  a  few  years  under  the  superintendence  of 
Capt.  Thomas  Martin.  A  shaft  has  been  suuk  300  feet  perpendicularly,  into  which  I 
descended  with  Captain  Martin.  The  old  bed,  whose  strike  was  nearly  NE.  and  SW., 
has  been  abandoned,  and  by  carrying  a  horizontal  shaft  260  feet  a  new  bed  was 
struck,  which,  at  the  place,  runs  nearly  IST.  and  S.  and  dips  west  about  45°.  The 
average  width  was  stated  to  be  15  feet,  and  in  some  places  23  feet.  If  this  be  not  a 
mere  protuberant  mass,  occasioned  by  lateral  pressure,  it  indicates  a  larger  amount  of 
coal  than  I  have  seen  in  any  other  mines  in  this  coal  field. 

8.  The  Valley  Falls  mine. — This  is  scarcely  more  than  a  mile  south  from  the 
Eoger  Williams  mine,  yet  the  strike  of  the  beds  will  not  allow  us  to  suppose  them 
connected.  The  operations  here  are  carried  on  by  the  Blackstone  Coal  Company.  A 
shaft  is  carried  down,  which  follows  a  bed  of  coal,  with  a  dip  near  the  surface  of  30°  to 
45°.  This  bed,  whicli  I  examined  several  years  ago,  to  a  depth  of  about  50  feet,  exposed 
a  thickness  of  coal  from  6  to  9  feet,  and  the  direction  was  IST.  50°  to  60°  E.  Since  that 
time  the  "incline,"  as  the  miners  call  it,  has  been  j)ushed  downward  500  feet,  or 
about  375  feet  of  perpendicular  depth,  and,  as  already  mentioned,  the  strata  have 
been  found  to  curve  very  much,  and  not  less  than  five  beds  of  coal  have  been  crossed, 
the  best  having  a  width  of  6  feet.     One  nest  of  coal  was  found  30  feet  square. 

9.  In  Seekonk. — I  am  informed  by  J.  IST.  Bolles,  esq.,  of  Providence,  that  the  out- 
crop of  a  bed  of  coal  was  found  in  digging  a  well  in  this  place,  only  15  feet  from  the 
surface.  Its  quality  was  similar  to  that  found  at  Valley  Falls.  In  the  same  region 
occur  very  fine  specimens  of  coal  plants,  especially  calamites. 

10.  In  Providence. — The  same  gentleman,  in  boring  for  water  in  the  north  part 
of  Providence,  at  the  depth  of  60  feet,  struck  a  bed  of  coal  dipping  NB.  45°,  which 
is  10  feet  thick,  and  of  the  same  general  character  as  that  at  Valley  Palls,  which  is 
known  to  burn  well. 

11.  In  Cranston,  Rhode  Island. — This  town  is  on  the  west  side  of  Narragansett 
Bay,  along  which  the  coal  rocks  extend  as  far  as  Wickford.  In  Cranston,  according 
to  Dr.  C.  T.  Jackson,  "slate,  graphite,  and  impure  anthracite"  are  found  in  an  excava- 
tion 7  or  8  feet  deep.  Coal  plants  are  very  abundant  on  Warwick  Neck,  but  no  coal 
has  been  found. 

12.  In  Bristol,  Rhode  Island. — The  coal  bed  in  this  place  is  in  the  west  part  of  the 
town,  and  the  spot  where  it  crops  out  is  only  a  few  feet  above  the  harbor.  It  was 
discovered  in  sinking  a  large  well.  Although  I  descended  into  it,  I  could  not  ascertain 
the  thickness  of  the  bed,  nor  with  accuracy  its  strike  and  dip.  Approximately  it  runs 
N.  a  few  degrees  E.,  and  dips  westerly  about  48°.  The  coal  did  not  appear  to  me  to 
be  as  much  crushed  as  in  some  mines,  and  seems  of  an  excellent  quality. 

13.  Portsmouth  mine,  or  Case's  mine,  in  Rhode  Island. — This  mine,  situated  in  the 
northeast  part  of  the  island  of  Rhode  Island,  was  opened  in  1808,  which  was  earlier 
than  the  Pennsylvania  mines  were  explored.  At  that  time  the  mode  of  burning 
anthracite  was  not  known,  and  the  coal  was  not  sought  after,  and  the  work  was 


OCCUERENCES  OF  COAL.  207 

abandoned  iu  1813  or  1814.  Some  years  afterwards  it  was  resumed,  and  in  1827, 
according  to  Mr.  Clowes,  the  agent,  20  men  and  5  boys  raised  about  1,100  tons  of 
coal,  coarse  and  fine.  But  the  work  was  again  abandoned  not  long  after,  and  not 
resumed  till  ISIT,  when  the  mine  was  opened  by  the  Portsmouth  Coal  Company,  which 
has  also  ceased  operations  there.  Mr.  Barbour  speaks  of  the  amount  of  coal  and 
rock,  "principally  the  former,"  that  has  been  excavated  at  this  place,  as  about 
100,000  tons. 

Three  beds  were  discovered  at  this  place,  "all  of  workable  width."  Dr.  C.  T. 
Jackson  says  that  the  bed  last  wrought  was  13  feet  thick.  He  states  its  strike  to  be 
S.  80°  W.  and  IST.  80°  E. ;  dip,  35°  southeasterly.  Mr.  Clowes,  however,  says  that  the 
beds  run  NE.  and  SW.  and  dip  from  40°  to  90°  southeast.  As  the  mine  is  now 
unwrought,  I  could  not  settle  these  points. 

14.  The  Aquidneclc  mine. — [In  the  account  of  this  mine  it  is  stated  that  three 
beds  of  coal  occur,  only  one  of  which,  from  2  to  20  feet  thick,  was  worked  by  the 
Aquidneck  Coal  Company.  The  middle  bed  was  followed  down  to  the  depth  of  020 
feet,  from  which  six  gangways  were  extended,  from  80  to  844  feet  each.  During  the 
last  half  of  1851,  3,100  tons  of  coal  were  taken  out,  and  an  opening  made  into  a  sub- 
jacent bed. — J.  B.  W.J 

15.  In  Neioport^  Rhode  Island. — [An  outcrop  of  coal  in  the  southeast  part  of  the 
town  is  described,  and  it  is  stated  that  during  the  Eevolutionary  war  the  British 
made  excavations  at  this  spot  in  search  of  fuel.  The  prospect  is  poor.  The  shale 
abounds  in  coal  plants. — Abstract  by  J.  B.  W.] ' 

Otlier  references  to  coal  will  be  found  on  pages  169,  182,  189,  190,  198. 

SEARCH    FOR    COAL. 

As  the  coal  beds  in  this  basin  are  mainly  concealed  in  depressions 
filled  with  drift,  or  have  their  outcrop  under  river  beds  and  swamps,  the 
details  of  this  report  are  mainly  useful  when  made  the  basis  of  a  process  of 
exclusion,  in  which  the  prospector  searches  along  lines  of  strike  between 
bands  of  strata  which  are  shown  to  be  barren.  So  far  as  can  be  ascer- 
tained from  field  evidence,  coal  beds  are  likely  to  be  found  in  the  greater 
part  of  the  field  outside  of  the  red  rocks  and  lenticular  areas  occupied  by 
the  upper  conglomerates,  which  together  do  not  occupy  an  area  greater 
than  3U  square  miles.  In  most  of  the  area  thus  left,  the  dip  of  the  beds  is 
low,  so  that  experimental  borings  are  likely  to  penetrate  several  strata. 
Where  the  strata  stand  at  a  high  angle  the  chance  of  meeting  with  coal 
beds  is  less  good,  although  they  may  exist  at  one  side  of  the  trial  boring  in 
the  same  field.     Such  a  belt  of  highly  inclined  strata  runs  north-northeast 

'  Mass.  House  Documents  No.  39,  March,  1853,  pp.  9-13. 


208 


GEOLOGY  OF  THE  NAREAGAI^TSETT  BASIK 


across  tlie  northwestern  part  of  the  Taunton  quadrangle,  through  Norton, 
in  the  vicinity  of  Providence,  and  along  the  lower  course  of  the  Warren 


Fig.  29.— Case  where  a  boriuK  w  ilie  iiio.st  economical  and  certain  metliod  ol  detonuiuiug  the  presence  of  a  series  of 
coal  beds  in  a  given  thickness  of  coal  measures. 

River  in  Swansea.     In  areas  of  vertical  strata,  trenching  across  the  upturned 
edges  of  the  beds  would  better  serve  the  purpose.     (See  figs.  29  and  30.) 


THICKTSESS   OF   THE   CARBONIFEROUS. 

There  are  but  few  cross  sections  of  the  strata  obtainable  in  the  Narra- 
gansett  Basin  which  are  so  far  free  from  the  perplexing  hindrances  set  forth 
in  the  introduction  to  this  report  that  the  geologist  can  with  confidence 


Fig.  30 Case  where  a  boring  may  miss  an  important  coal  bed  and  is  not  likely  to  discover  more  than  one,  and 

w  here  a  trench  at  right  angles  to  the  strike  would  reveal  the  true  number  of  seams  of  coal. 

give  an  estimate  of  the  thickness  of  the  beds  entering  into  them.  The 
most  satisfactory  line  of  section  in  the  northern  part  of  the  basin  passes 
from  the  southern  margin  through  the  Dighton-Swansea  and  Great  Meadow 
Hill  or  Taunton  synchnes  toward  Mansfield  and  the  northern  border.  The 
general  relations  of  the  structure  along  this  line  are  shown  in  fig.  8  (p.  122). 
Measurements  along  this  line  give  about  12,000  feet  as  the  thickness  of  the 


THICKNESS  OF  THE  GARBONIPEEOUS.  209 

strata  between  the  granitic  base  and  the  top  of  the  Dighton  group.  The 
evidence  on  which  this  estimate  is  based  is  as  follows : 

From  the  south  bank  of  the  Taunton  River  north  of  Steep  Brook  to 
the  axis  of  the  Dighton-Swansea  syncline  there  is  a  section  from  the  base 
to  the  uppermost  beds  of  the  series.  The  distance  along  this  line  perpen- 
dicular to  the  strike  is  approximately  3  miles,  and  the  dip  of  the  beds  is 
generally  steep;  it  may  be  assumed  to  be  as  high  as  45".  This  gives  11,198 
feet  as  the  thickness  of  the  strata  remaining  along  this  margin  of  the  basin. 

Between  the  axes  of  the  Dighton-Swansea  and  the  Taunton  synclines 
is  a  distance  of  6  miles.  The  intervening  beds,  in  anticlinal  position, 
though  very  imperfectly  exposed,  nowhere  exhibit  in  the  few  exposures 
available  for  interpretation  foldings  or  thrusts  likely  to  diminish  or  increase 
the  estimate  of  thickness  based  on  measurements  across  the  interval  between 
the  two  synclinal  axes.  The  dips  on  the  southern  side  of  the  anticlinal 
axes  are  very  steep,  mainly  above  45°;  the  dips  on  the  northern  side  are 
much  less  steep,  mainly  below  45°.  The  lowest  beds  exposed  anywhere 
along  the  anticlinal  axis  lie  above  the  basal  beds  of  the  Carboniferous; 
so  that  estimates  along  this  line  must  necessarily  fall  short  of  the  base. 
Assuming  45°  as  the  avei'age  dip  over  this  anticlinal  section,  and  since  the 
beds  over  half  the  distance  between  the  adjacent  synclines  have  3  miles  of 
outcrop  as  before,  we  obtain  the  same  amount  as  on  the  southern  side  of  the 
Dighton-Swansea  syncline.  Inasmuch  as  this  estimate  of  about  11,200 
feet  is  a  minimum  and  does  not  reach  the  base,  it  is  probable  that  the  beds 
increase  in  thickness  toward  the  middle  and  now  deeper  part  of  the  basin. 

Northward  from  the  Taunton  syncline  to  the  northern  border  near 
Mansfield  there  is  certainly  one  anticlinal  area,  and  another  syncline  in 
the  Mansfield  coal  basin ;  but  there  are  no  exposures  of  the  upper  conglom- 
erate series  along  this  line,  and  the  outcrops  are  totally  inadequate  for 
making  even  minimum  estimates  of  thickness. 

West  of  the  line  of  section  above  described  an  aj^proximate  estimate 
of  thickness  can  be  founded  upon  the  strata  exposed  between  the  western 
end  of  the  Taunton  syncline  in  Seekonk  and  the  axis  of  the  Attleboro  syn- 
cline. From  the  Perrin's  anticline,  where  there  is  a  probable  overthrust  of 
the  beds  on  the  south,  to  the  axis  of  the  adjacent  Attleboro  syncline  there 
is  a  fairly  continuous  exposure  of  outcrops,  ranging  in  inclination  from  45°, 
for  a  few  hundred  feet  on  the  south,  to  nearly  vertical  for  most  of  the 

MON  xxxiii 14 


210  GEOLOGY  OF  THE  NAERAGANSETT  BASIN. 

remaining  distance  to  tlie  Attleboro  synclinal  axis.  Assuming  75°  as  the 
average  dip  across  these  upturned  beds,  which  have  a  breadth  of  outcrop  of 
about  11,900  feet,  -we  obtain  about  11,500  as  a  measurement  of  the  thick- 
ness. Again  this  is  a  minimum  estimate,  reaching  only  from  the  top  of  the 
highest  remaining  beds  in  the  synclinal  trough  to  the  lowest  exposures  in 
a  broken  anticlinal  arch. 

These  measurements,  taken  in  the  northern  part  of  the  basin,  across 
comparatively  simple  great  folds,  enforce  the  conviction  that  the  strata  now 
remaining  in  the  deeper,  central  portion  of  this  basin  can  not  be  less  than 
12,000  feet  in  thickness.  This  estimate  agrees  closely  with  that  given  for 
the  Carboniferous  strata  of  the  Joggins  section  in  Nova  Scotia,  which  are 
about  13,000  feet  thick. 


U.S. GEOLOGICAL  SURVEY 


MONOGRAPH    XXXIll,    PL.      XVII 


GEOLOGICAL  M/\P  OF  THE  NORTHEM  AND  EASTERN  PORTIONS  OF  THE  NARRAGM^SETT  BASIN 

llY.I.Ti.WOODWdKTH,  ASSISTANT  (H'JJLOOIST.  M.S.  SHALKH.GKdl.dClsl'  IX  I  IIAIKiK 
Scale 


LEGEND 

SEDIMENTARY  ROCKS 


^     s 


IGNEOUS  ROCKS 


^^\ 


Diabase  dikes 


Quartz-porpMn 


Fa  nils 

OUTCROPS 


ACKNOWLEDGMENTS. 

I  wish  to  express  my  indebtedness  to  my  associates  in  this  work  for 
much  guidance  and  aid,  both  in  the  field  and  in  the  hiboratory,  and  particu- 
larly to  Dr.  Foerste  for  many  suggestions  and  actual  aid  in  delimiting 
the  Cambrian,  Carboniferous,  and  igneous  rocks  about  North  Attleboro. 
The  follo^ying-named  gentlemen  rendered  assistance  at  one  time  or  another 
during  the  course  of  the  field  work:  C.  W.  Coman,  U.  S.  G.  S.;  Robert 
Wainwright,  W.  E.  Parsons,  Harry  Landes,  U.  S.  G.  S.;  J.  Ralph  Finlay, 
U.  S.  G.  S.,  and  G.  W.  Tower.  To  Prof  J.  E.  Wolff  my  thanks  are  due 
for  examining  many  thin  sections  of  rocks.  To  Prof  George  H.  Barton  I 
am  indebted  for  the  privilege  of  reading  a  manuscript  report,  with  sections, 
based  upon  his  study  of  the  Norfolk  County  Basin,  and  to  Prof  A.  S. 
Packard,  of  Brown  University,  for  the  use  of  the  collection  of  plants  from 
Rhode  Island.  All  the  photographs  illustrating  this  monograph  were  taken 
under  my  immediate  supervision  by  Mr.  Philip  P.  Sharpies,  of  Cambridge, 
Massachusetts. 


APPENDIX. 

BIBLIOGRAPHY   OF  THE  CAMBRIAN  AND  CARBONIFEROUS   ROCKS  OF 
THE  NARRAGANSETT  BASIN. 

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Massachusetts  Institute  of  Technology,  Boston,  Massachusetts,  1880, 63  pp. 

and  Crosby,  W.  O.    See  Crosby,  W.  O. 

Battey,  T.  J.    See  Providence  Franklin  Society. 

Beche,  de  la,  H.     A  geological  manual,  Philadelphia,  1832,  pp.  401, 404. 

Blake,  W.  P.    The  plasticity  of  pebbles  and  rocks.     Proc.  Am.  Acad.  Arts  Sci.,  vol. 

18,  1869,  pp.  199-205. 
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Hist.  Soc,  Vol.  II,  1883-84,  pp.  9-12. 
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Vol.  X,  1894-95,  pp.  199-230;  map,  pi.  iv. 
Cozzens,  Issachar.    A  geological  histoiy  of  Manhattan  or  New  York  Island,  New 

York,  1843,  pp.  60-64,  pi.  vi. 
Crosby,  W.  O.    Contributions  to  geology  of  eastern  Massachusetts,  1880. 
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Am.  Jour.  Sci.,  3d  series,  Vol.  XX,  1880,  pp.  416-420. 
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Vol.  XXIII  [1886],  pp.  325-330. 
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Nat.  Hist.,  Vol.  XXII,  1883,  pp.  179-201  pis.  i-iii.    Partial  bibliography  given, 

pp.  180-182.    Also  the  geology  of  the  tract  known  as  Paradise,  near  Newport. 

Proc.  Newport  Nat.  Hist.  Soc,  1883-84,  Doc.  2,  pp.  3-5,  2  pis. 
Eemarks  on  some  of  the  evidences  of  geological  disturbance  in  the  vicinity  of 

Newport.    Proc.  Newport  Nat.  Hist.  Soc,  1883-84,  Doc.  2,  pp.  5-8. 
The  geology  of  the  mouth  of  Narragansett  Bay.     Proc.  Newport  Nat.  Hist.  Soc, 

1884-85,  Doc.  3,  May,  1885,  pp.  5-14. 
On  metamorphism  in  the  Ehode  Island  coal  basin.     Proc.  Newport  Nat.  Hist. 

Soc,  1884-85,  Doc.  3,  1885,  pp.  84-86. 
A  contribution  to  the  geology  of  Ehode  Island.    Am.  Jour.  Sci.,  3d  series.  Vol. 

XXVII,  1884,  pp.  217-228, 282-291.     Also  Proc.  Canadian  Inst.,  1884-85,  p.  21. 
List  of  minerals  and  rocks  occurring  in  the  vicinity  of  Newport.    Proc.  Newport 

Nat.  Hist.  Soc,  1886-87,  Doc.  5,  pp.  29-31. 
Dana,  J.  D.    Manual  of  geology,  3d  edition,  1880,  pp.  314-315. 

Manual  of  geology,  4th  edition,  1895,  p.  657. 

Archean  axes  of  eastern  North  America.    Am.  Jour.  Sci.,  3d  series,  Vol.  XXXIX, 

1890,  pp.  378-388.     P.  380. 
212 


BIBLIOGEAPHY.  213 

Davis,  W.  M.    The  physical  geography  of  southeru  Xew  Eu  gland.     Nat.  Geog.  Mono- 
graphs, I,  1895,  No.  9,  36  pp. 

See  Shaler,  N.  S. 

Day,  S.     Anthracite  in  Wreutham,  Mass.     Am.  Jour.  Sci.,  3d  series,  Vol.  XXIII, 

1833,  p.  405. 
De  la  Beche.    See  Beche,  de  la,  H. 
Dodge,  W.  W.    Xotes  on  the  geology  of  eastern  Massachusetts.     Proc.  Boston  Soc, 

Nat.  Hist.,  Vol.  XVII,  1875,  pp.  388-419. 
Eaton,  Amos.    Argillite  embracing  anthracite  coal.     Am.  Jour.  Sci.,  1st  series,  Vol, 

XVI,  1829,  pp.  299-301. 
Emmons,  A.  B.    Notes  on  the  Rhode  Island  and  Massachusetts  coals.     Trans.  Am. 

Min.  Eng.,  Vol.  XIII,  1885,  pp,  510-517. 
Foerste,  Aug.  F.    The  igneous  and  metamorphic  rocks  of  the  Narragansett  Basin. 

Manuscript  thesis  deposited  in  the  library  of  Harvard  University,  1890. 

■ See  Shaler,  N.  S, 

Haldeman,  S.  S.    See  Taylor,  E.  G. 

Hitchcock,  C.  H.    Geology  of  the  island  of  Aquidneck.     Proc.  Am.  Ass.  Adv.  Sci., 

Vol.  XIV,  1860,  pp.  121-137. 
Synchronism  of  the  coal  beds  in  New  England  and  in  the  western  United  States. 

Proc.  Am.  Ass.  Adv.  Sci.,  Vol.  XIV,  1860,  pp.  138-143. 
The  distortion  and  metamorphism  of  pebbles  in  conglomerates.     Proc.  Am.  Ass. 

Adv.  Sci.,  Vol.  XVI,  1867,  pp.  124-127. 
Geological  map  of  Massachusetts.     Walling  and  Gray's  Atlas  of  Massachusetts, 

1871,  20  pp. 
Hitchcock,  Edward.     Eeport  on  the  geology  of  Massachusetts,  1833. 

Final  report  on  the  geology  of  Massachusetts,  1841,  831  pp. 

Eeport  to  the  governor  of  Massachusetts  on  certain  points  in  the  geology  of 

Massachusetts,  with  a  map  of  the  Bristol  and  Ehode  Island  coal  field.     Mass. 

House  Doc.  No.  39,  1853. 
The  coal  field  of  Bristol  County  and  Ehode  Island.     Am.  Jour.  Sci.,  2d  series. 

Vol.  XVI,  1853,  pp.  327-336. 
HoUey,  A.  L.    Notes  on  the  iron  ore  and  anthracite  coal  of  Ehode  Island  and  Massa- 
chusetts.    Trans.  Am.  Inst.  Min.  Eng.,  Vol.  VI,  1877,  pp.  224-227. 
Jackson,  C.  T.    Geology  and  agriculture  of  Ehode  Island,  1840. 
Lesquereux,  Leo.    Description  of  the  coal  flora  of  the  Carboniferous  formation  in 

Pennsylvania  and  throughout  the  United  States.    Second  Geol.  survey  of  Penn., 

Eeport  of  Progress,  P,  Vol.  Ill,  1884,  pp.  867-868. 
The  Carboniferous  flora  of  Ehode  Island.    Am.  Naturalist,  Vol.  XVIII,  1884, 

pp.  921-923. 
Lyman,  B.  S.    Against  the  supposed  former  plasticity  of  the  puddingstone  pebbles 

of  Purgatory,  E.  I.    Proc.  Am.  Assoc.  Adv.  Sci.,  Vol.  XV,  1867,  p.  83. 
Maclure,  Wm.    Observations  on  the  geology  of  the  United  States,  1817,  map.   ' 
Marcou,  Jules.    Lower  and  Middle  Taconic.    Am.  Geologist,  Vol.  VI,  1890,  pp.  97-98. 
Pirsson,  L.  V.    On  the  geology  and  petrography  of  Conanicut  Island,  E.  I.    Am. 

Jour.  Sci.,  3d  series.  Vol.  XLVI,  1893,  pp.  363-378. 
Providence  Franklin  Society.    Eeport  on  the  geology  of  Ehode  Island,  Providence, 

1887,  pp.  130.    Addenda,  1888,  pp.  131-132.    Gives  numerous  references  to  local 

newspaper  accounts. 


214  GEOLOGY  OF  THE  Is^AERAGAlsrSETT  BASIN. 

Rogers,  W.  B.     [Elongation  of  pebbles  in  conglomerate  at  Purgatory,  near  Newport, 

K.  I.,  and  elsewhere.]     Proc.  Boston  Soc.  Nat.  Hist.,  Vol.  VII,  1860,  pp.  391-394. 
[Shells  in  siliceous  slate  pebbles  in  the  drift  at  Fall  Kiver,  etc.]     Proc.  Boston 

Soc.  Nat.  Hist.,  Vol.  VII,  1860,  pp.  389-391. 
On  the  Newport  conglomerate.    Proc.  Boston  Soc.  Nat.  Hist.,  Vol.  XVIII,  1875, 

pp.  97-101. 
Salisbury,  Charles  M.     See  Providence  Franklin  Society. 
Shaler,  N.  S.     On  the  geology  of  the  island  of  Aquidneck  and  the  neighboring  shores 

of  Narragansett  Bay.    Am.  Naturalist,  Vol.  VI,  1872,  pp.  518-528;  611-621; 

751-760. 
Note  on  the  geological  relations  of  the  Boston  and  Narragansett  bays.    Proc. 

Boston  Soc.  Nat.  Hist.,  Vol.  XVII,  1875,  pp.  188-490. 
On  the  geology  of  the  Cambrian  district  of  Bristol  County,  Mass.     Bull.  Mus. 

Comp.  Zool.  Harvard  Coll.,  Vol.  XVI,  No.  2,  1888,  pp.  13-20,  map. 
and  Foerste,  A.  F.     Preliminary  description   of  North  Attleborough  fossils. 

Bull.  Mus.  Comp.  Zool.  Harvard  Coll.,  Vol.  XVI,  No.  2,  1888,  pp.  27-41,  2  pis. 
Shurrocks,  T.  H.     See  Providence  Franklin  Society. 
Taylor,  E.  C,  and  Haldeman,  S.  S.     Statistics  of  coal,  etc.,  2d  ed.,  Philadelphia, 

1854,  p]).  446-456. 
Teschemacher,  J.  E.     On  the  fossil  vegetation  of  America.     Boston  Jour.  Nat.  Hist., 

Vol.  V,  1846,  pp.  370-385. 
Vanuxem,  L.     Experiments  in  anthracite,  plumbago,  etc.     Am.  Jour.  Sci.,  1st  series. 

Vol.  X,  1826,  pp.  104-105. 
Wadsworth,  M.  E,    A  microscopical  study  of  the  iron  ore,  or  peridotite,  of  Iron 

Mine  Hill,  Cumberland,  li.  I.     Bull.  Mus.  Comp.  Zool.   Harvard  Coll.,  Vol. 

VII,  1881,  No.  4,  pp.  183-187. 
Walcott,  C.  I).     Position  of  the  Olenellus  fauna.     Am.  Jour.  Sci.,  3d  series.  Vol. 

XXXVII,  1889,  pp.  387-388. 

The  Olenellus  fauna.     Tenth  Ann.  Kept.  U.  S.  Geol.  Survey,  Part  I,  1890,  p.  567. 

Note  on  the  brachiopod  fauna  of  the  quartzitic  pebbles  of  the  Carboniferous  con- 
glomerates of  the  Narragansett  Basin,  Rhode  Island.    Am.  -Jour.  Sci.,  4th  series. 

Vol.  VI,  1898,  pp.  327-328. 
Ward,  L.  F.     Distribution  of  fossil  plants.     Eighth  Ann.  Bept.  F.  S.  Geol.  Survey, 

Part  II,  1889,  p.  853. 
Wood-worth,  J.  B.     Carboniferous  fossils  in  the  Norfolk  County  Basin.     Am.  Jour. 

Sci.,  3d  series,  Vol.  XLVIII,  1894,  pp.  145-148. 


GEOLOGY  OF  THE  NARRAGANSETT  BASIN 


Part    III.— THE    CARBONIFEROUS    STRATA    OF    THE 
SOUTHVi/ESTERN    PORTION    OF    THE    BASIN 

WITH 

AN  ACCOUNT  OF  THE  CAMBRIAN  DEPOSITS 

By    A.XJC-.    F.    FOERSTE 


CONTENTS. 


Page. 

Chaptek  I. — Introduction 223 

Difficulties  of  the  field 223 

Arraugemeut  of  report 225 

Chapter  II. — The  western  islands  of  the  hay 227 

Dutch  Island 227 

Conanicut  Island 228 

Fox  Hill,  Beaver  Head 228 

Northern  half  of  the  island,  north  of  Round  Swamp 229 

Southern  half  of  the  island,  south  of  Round  Swamp 23£ 

Shale  region 232 

Granite  area,  the  Dumplings,  and  arkose  region  west  of  the  Dumplings 233 

Hope  Island 235 

Prudence  Island 237 

Chapter  III. — The  western  shore  of  the  bay 242 

From  Sauuderstown  to  Narragansett  Pier 242 

Along  the  shore 242 

West  of  the  cove  and  Pattaquamscott  River 246 

From  Saunderstown  to  Wickford 248 

From  Wickford  to  East  Greenwich 251 

Western  border  of  the  Carboniferous  basin,  from  East  Greenwich  to  Natick  and  north- 
ward into  Cranston 252 

Rocks  east  of  the  western  border  of  the  Carboniferous  area  in  Warwick  and  southern 

Cranston 256 

Warwick  Neck 258 

Chapter  IV. — The  northern  shore  of  the  bay 259 

Providence  River  and  eastward 259 

Rumstick  Neck 260 

Popasquash  Neck 261 

Bristol  Neck  261 

Carboniferous  area 261 

Granite  area 262 

AVarreu  Neck 264 

Conglomerates  and  shales  of  Swansea  and  Warren,  north  of  the  necks 264 

Gardeners  Neck 267 

Braytons  Point  and  northward 268 

Se wammock  Neck 268 

Chapter  V. — The  eastern  shore  of  the  bay 269 

Steep  Brook 269 

Fall  River 270 

Townsend  Hill 270 

Tiverton  271 

Gould  Island 272 

Granite  area  at  the  northeast  eud  of  Aquidneck  Island... 273 

Eastern  border  of  the  Carboniferous  basin  south  of  Tiverton  Four  Corners 274 

Sandstone  series  between  Windmill  Hill  and  the  cove  north  of  Browns  Point 275 

217 


218  CONTENTS, 

Chapter  V. — The  eastern  shore  of  the  bay — Continued.  Page. 

Coarse  conglomerate  series  along  the  east, shore  of  Sakonnet  River 278 

High  Hill  Point 278 

Fogiand  Point 278 

Exposures  west  of  Nonquit  Pond  . .-. 279 

Exposures  between  Tiverton  Four  Corners  and  the  northeast  side  of  Nanniiquacket 

Pond 280 

Little  Compton  shales - 281 

Chapter  VI. — Aquidneek,  or  the  Island  of  Rhode  Island,  with  the  islands  of  Newport  Harbor. .  284 

Arkose  and  pre-Carboniferous  rooks  on  Sachuest  Neck 28i 

Arkose 284 

Pre-Carboniferous  rocks 286 

Eastern  shore  of  A(iuidueck  Islaud  as  far  south  as  the  second  cove  northvrest  of  Black 

Poiut -..- 288 

Coarse  conglomerates  and  underlying  sandstone  series  from  Black  Point  to  the  north  end 

of  Smiths  Beach  ---- 290 

Coarse  conglomerates  and  underlying  rocks  on  the  neck  at  Eastons  Point 294 

Paradise  coarse  conglomerates - 295 

Paradise  rocks 295 

The  Hanging  Rocks 298 

Pre-Carboniferous  area - 300 

Isolated  conglomerate  exposures  near  Eastons  Pond  and  northward 303 

Miantonomy  Hill  and  Coasters  Harbor  Island  conglomerates 304 

Miantonomy  Hill 304 

Beacon  Hill 304 

Field  exposures  of  coarse  conglomerates 304 

Coddington  Neck 305 

Bishop  Rock 305 

Coasters  Harbor  Island 

Newport  Harbor  Islands 307 

Gull  Rocks -- 307 

Rose  Island 308 

Conanicut  Island - 308 

Line  of  separation  between  Carboniferous  and  pre-Carboniferous  rocks 308 

Goat  Island  and  Little  Lime  Rock 309 

Fort  Greene 309 

Morton  Park  and  southward 309 

Northeast  lines  of  possible  faulting 310 

Carboniferous  rocks  along  the  Newport  Cliffs 310 

Newport  Neck  and  southern  cliff  rocks 314 

Greenish  igneous  rock  in  the  cliffs  southwest  of  Sheep  Point 314 

Granite  area  at  the  south  end  of  the  cliffs 315 

Granite  area  on  eastern  Newport  Neck 316 

Greenish  and  purplish  argillitic  rock  of  middle  Newport  Neck 316 

Pre-Carboniferous  green  and  purple  shales  of  western  Newport  Neck 316 

Shale  series  from  Coddington  Cove  to  Lawtons  Valley 319 

Greenish-blue  shales  of  Slate  Hill  and  southward 320 

Shale  series  north  of  Lawtons  Valley 320 

Shore  exposures  north  of  Coggoshall  Point 320 

Portsmouth  mine  and  northeastward 321 

Line  of  exposures  three-eighths  of  a  mile  west  of  the  Newport  road 326 

Shale  series  at  Butts  Hill 327 

Green  shales  and  conglomerates  of  the  northern  syncline 327 

Green  shales  along  the  western  Newport  road 327 

Portsmouth  conglomerates 328 

Relations  to  Slate  Hill  shales 329 


CONTENTS.  219 


Chapter  VII. — The  Kingstowu  series 331 

Unity  and  Hthological  character  of  the  Kingstown  sandstone  series 331 

Section  from  the  Bonnet  to  Boston  Neck 333 

Section  from  the  Bonnet  to  Hazard's  quarry  and  Indian  Corner 333 

Kingstown  series  in  southwestern  Cranston  and  western  Warwick 334 

Probable  thickness  of  the  Kingstown  sandstone  series  in  Cranston  and  Warwick. ..  336 

AVarwick  Neck  exposures 386 

Exposures  on  the  western  islands  of  the  bay 337 

Thickness  of  strata  between  the  Bonnet  and  Dutch  Island 337 

Lithology  of  the  Dutch  Island  series 338 

Beaver  Head  section 338 

Total  thickness  of  Kingstown  series,  including  the  conglomerate  at  Beaver  Head..  338 

Western  shore  of  Conanicut 339 

Eastern  shore  of  Conanicut 339 

Probable  folding  in  the  northern  part  of  Conanicut  Island 340 

Hope  Island 341 

Kingstown  series  exposures  on  the  western  islands 342 

Prudence  Island 342 

Western  Bristol  Neck 343 

Eumstick  Neck 344 

Kingstown  sandstones  equivalent  to  lower  part  of  Coal  Measures  group 344 

Triangular  area  of  the  Kingstown  series  in  the  Narragansett   Basin,  narrowing 

southward 344 

Thickness  of  the  series  and  evidence  of  folding 345 

Rocky  Point  conglomerate  and  its  connection  with  the  estimate  of  the  thickness  of 

the  northern  section 346 

Chief  features  of  the  Kingstown  series 346 

Fossil-plant  localities 347 

Chapter  VIII. — The  Aquidneck  shales 348 

Area  occupied  by  the  Aquidneck  shale  series 348 

Southern  Conanicut 349 

Prudence  Island 350 

Thickness  of  shale  series  on  each  side  of  Prudence  Island  syncliue 351 

Bristol  Neck 351 

Aquidneck  Island 352 

Thickness  of  the  shale  section  east  of  the  Portsmouth  syncline 353 

Probable  thickness  of  the  shale  section  west  of  the  Portsmouth  syncline 353 

Lithological  variations  in  the  shale  series 354 

Geological  structure  of  the  middle  third  of  Aquidneck  Island 354 

Strata  probably  folded 355 

Gould  Island  of  the  Middle  Passage 356 

.  Southern  third  of  Aquidneck  Island 356 

Upper  green  shales  of  the  Aquidneck  series 356 

Sakonnet  sandstones  of  the  Aquidneck  series  west  of  the  river 357 

Thickness  of  the  upper  green  shales 357 

Thickness  of  the  Sakonnet  sandstones 358 

Northern  extension  of  the  Aquidneck  shales 358 

Equivalents  of  Kingstown  sandstone  and  Aquidneck  shale  series  northeast  of  Warren  Neck.  358 

Sakonnet  sandstones  on  the  oast  side  of  the  river 359 

Absence  of  the  shale  series  beneath  the  coarse  conglomerates  east  of  the  Sakonnet  River  . ..  360 

AVedge-shaped  areal  distribution  of  the  Aquidneck  shale  series 361 

Equivalence  of  the  Kingstown  sandstones  and  the  Aquidneck  shales 361 

Fossils  of  the  Aquidneck  shale  series 363 


220  CONTENTS. 

Paffe. 

Chaptee  IX.— The  Purgatory  conglomerate 364 

Coarse  conglomerate  overlying  the  Aquidneck  shale  series 364 

Sakonnet  sandstones  within  the  Aquidneck  shales,  in  transition  to  the  coarse  con- 
glomerate    365 

Coarse  conglomerate  forming  the  latest  Carboniferous  rocks  in  the  southern  part 

of  the  Narragansett  Basin 365 

Purgatory  conglomerate  as  a  typical  exposure 365 

Identity  of  the  Purgatory  and  Sakonnet  River  western  shore  coarse  conglomerate. ..  366 

Possible  syncline  between  the  two  western  Paradise  ridges  of  conglomerate 366 

Hanging  Eock  ridge  possibly  the  eastern  side  of  an  anticlinal  fold 367 

Dips  immediately  east  of  Hanging  Rock  ridge 367 

Interpretation  adopted 367 

Southward  pitch  of  the  great  Paradise-Hanging  Rock  syncline 368 

Southward  pitch  of  the  Sakonnet  River  syncline 369 

Western  coarse  conglomerate  exposures 369 

Possible  syncline  immediately  west  of  Miantonomy  Hill 369 

Possibility  of  two  horizons  of  conglomerate  at  Miantonomy  Hill 370 

Interpretation  adopted 371 

Geological  position  of  the  Newport  Cliff  section 371 

Portsmouth  synclinal  conglomerate 373 

Conglomerates  of  Warwick  Neck  and  Swansea 373 

Thickness  of  the  coarse  conglomerate 373 

Fossil  localities 374 

Chapter  X. — The  arkoses  and  basal  conglomerates 375 

Natick  arkose 375 

From  Natick  to  Cranston 375 

Base  of  the  Carboniferous  south  of  Natick 376 

Probable  relations  between  the  various  granites  and  pegmatites  and  the  Carbon- 
iferous beds 376 

Tiverton  arkose 378 

From  Steep  Brook  to  Nannaquacket  Pond 378 

South  of  Nannaquacket  Pond 379 

Equivalence  Of  the  Tiverton  arkoses  to  those  near  Natick 379 

Sachuest  arkose ■ 379 

Conanicut  arkose 380 

Rose  Island  and  Coasters  Harbor  Island  arkose 380 

Chapter  XI. — The  pre-Carboniferous  rocks  of  the  southwestern  portion  of  the  Narragansett 

Basin 381 

Little  Compton  and  Newport  Neck  shales 383 

Quartzites  of  Natick 383 

Chapter  XII. — The  Cambrian  strata  of  the  Attleboro  district 386 

Cambrian  brook  localities 388 

Localities  1  and  2,  southwest  of  North  Attleboro 388 

Valley  of  locality  3 392 

Locality  4,  northeast  of  Diamond  Hill 393 

Maps  and  sections 394 


ILLUSTRATIONS. 


XVIII.  Contact  of  pegmatites  witli  Kingstown  shales,  Watsons  Pier,  Rhode  Island 242 

XIX.  Coarse  pegmatites  of  AVatsons  Pier,  Rhode  Island 244 

XX.  Cross-stratification  in  pebbly  sandstone  of   Kingstown   series,    Devils  Foot 

Ledge,  Rhode  Island 248 

XXI.  Sandstone-gneiss  of  Kingstown  series,  Devils  Foot  Ledge,  Rhode  Island 334 

XXII.  Stratification  and  slaty  cleavage,  Aquidneck  shales,  eastern  shore  of  Prudence 

Island 350 

XXIII.  Wave-cut  bench  in  Aquidneck  shales,  western  shore  of  Prudence  Island 35S 

XXIV.  Fretwork  weathering  of  Aquidneck  shales,  Prudence  Island 362 

XXV.  Pegmatite  dikes  cutting  Kingstown  shales,  Watsons  Pier,  Rhode  Island 376 

XXVI.  Hoppin    Hill,   a  granite  mass  surrounded  by   Cambrian,    North  Attleboro, 

Massachusetts 38t 

XXVII.  Sketch  map  of  the  North  Attleboro  Cambrian  localities 388 

XXVIII.  Sections  in  the  Narragansett  Bay  region 394 

XXIX.  Sections  in  the  Narragansett  Bay  region 394 

XXX.  Sections  in  the  Narragansett  Bay  region 394 

XXXI.  Geological  map  of  the  southern  part  of  the  Narragansett  Basin 394 

221 


GEOLOGY  OF  THE  NARRAGANSETT  BASIN. 

PART  IIL-THE  SOUTHWESTERN  PORTION  OP  THE  BASIN. 


B)^  Aug.  F.  Foerste. 

CHAPTER   I. 

INTRODUCTION. 

DIFFICULTIES  OF  THE  FIELD. 

The  writer  first  studied  the  geology  of  the  Narragansett  Basin  in  the 
summer  of  1887.  Thereafter  he  spent  a  part  of  each  summer  in  this  field 
imtil  1890.  His  investigations  during  this  time  were  confined  almost 
entirely  to  the  region  around  North  Attleboro,  and  some  attention  was 
given  to  tracing  the  present  margin  of  the  Carboniferous  basin.  In  the 
course  of  the  latter  Avork  about  three  months  were  spent  on  the  southern 
half  of  the  Carboniferous  basin.  Some  of  these  studies  Avere  recorded  in 
a  thesis,  "On  the  Igneous  and  Metamorphic  Rocks  of  the  Narragansett 
Basin,"  1890,  deposited  in  the  library  of  Harvard  College.  In  the  early 
summei  of  1890  a  short  stay  at  Newport  convinced  the  writer  that  an  order 
of  succession  of  the  Carboniferotis  rocks  could  be  made  out,  having-  the 
following  character:  (1)  At  the  base  a  series  of  shales,  now  known  as  the 
Aqnidneck  shales;  (2)  above  these,  sandstone  beds  with  some  small  pebbled 
conglomerates,  now  known  as  the  Sakonnet  beds;  (3)  a  verj^  coarse  peb- 
bled conglomerate,  then  already  known  as  the  Purgatorv  conglomerate. 
He  then  went  to  Swansea,  around  the  margin  of  the  great  Dighton  con- 
glomerates, in  order  to  see  whether  a  similar  succession  could  be  made  out 

223 


224  GEOLOGY  OP  THE  ISTAERAGAI^SETT  BASIN. 

there.  While  in  the  midst  of  this  work  he  was  called  away  fi'om  this  field 
to  another  division  of  the  Survey.  Only  about  four  months  had  therefore 
been  spent  by  the  writer  in  this  southern  portion  of  the  basin  previous  to 
the  present  summer  (1895),  when  two  additional  months  were  occupied  in 
field  work.  This  report  is  the  outcome  of  the  observations  made  at  these 
various  times.  No  one  can  understand  better  than  the  writer  both  the  short- 
comings of  the  report  and  the  difficulties  of  the  field.  While  exposures  are 
numerous  in  various  parts  of  the  basin,  chiefly  along  the  shores  of  the  main- 
land and  the  numerous  islands,  they  are  so  widely  separated  by  the  arms 
of  the  bay  and  by  broad  areas  of  sandy  soil  that  an  interpretation  of  the 
structural  relations  existing  between  the  exposed  rocks  is  exceedingly  diffi- 
cult, if  not  impossible.  Under  the  circumstances,  however,  it  is  hoped  that 
the  report  will  at  least  add  something  to  our  knowledge  of  the  basin  and 
furnish  a  basis  for  future  labors  and  rectifications. 

As  the  result  of  much  thought  and  care  in  the  study  of  the  exposures 
actually  found,  although  within  a  limited  time,  the  writei'  will  express  the 
following  opinions:  Isolated  exposures  of  small  extent,  unless  within  an 
area  of  frequent  exposures,  are  apt  to  be  more  misleading  than  serviceable 
in  the  identification  of  horizons,  owing  to  locally  sitdden  lithological 
changes,  especially  in  areas  occupied  by  the  Kingstown  series.  Greatest 
weight  in  making  out  geological  horizons  and  the  order  of  succession  should 
always  be  given  to  long  lines  of  exposure.  It  is  not  considered  advisable 
to  attempt  a  division  of  the  Carboniferous  rocks  into  separate  geological 
horizons  until  an  acquaintance  is  made  with  the  scattered  Carboniferous 
exposiu-es  over  a  very  large  area — in  fact,  over  at  least  half  of  the  area 
investigated — since  otherwise  the  importance  of  features  of  only  local  value 
is  easily  magnified. 

It  may  seem  trite  to  express  such  opinions,  in  view  of  the  advanced  state 
of  methods  of  geological  investigation,  but  these  remarks  are  especially 
pertinent  to  the  Narragansett  Basin,  where  the  investigator  of  a  limited 
field,  especially  in  the  dubious  country  in  southern  Aquidneck,  is  liable  to 
go  astray  on  account  of  the  absence  of  exposures  at  very  critical  points. 
Nowhere  are  isolated  small  exposures  more  liable  to  influence  opinion  as 
to  the  geological  succession  of  neighboring  larger  rock  masses  than  here, 
and  nowhere  is  the  possibility  of  consequent  erroneous  views  greater,  but 
the  attempt  has  been  made  to  overcome  these  difficulties,  and  it  is  hoped 
with  at  least  a  measure  of  success. 


mTKODDCTlOK  225 

ARRANGEMENT   OF  REPORT. 

A  reference  to  the  accompanying  map  (PI.  XXXI),  illustrating  the 
geology  of  the  lower  part  of  the  Narragansett  Basin,  will  show  that  more 
than  half  of  the  area  investigated  is  covered  by  the  waters  of  Narragansett 
Bay  and  its  many  ramifications,  A  large  part  of  the  remaining  area,  especi- 
ally along  the  shore  and  on  certain  islands,  is  covered  by  sand  and  various 
glacial  and  more  recent  deposits.  The  rock  exposures  occur  chiefly  along 
the  shore  Much  of  the  geology  is  necessarily  uncertain,  and  the  writer 
claims  only  such  an  advance  in  the  knowledge  of  the  geological  features  of 
the  region  as  a  careful  study  of  the  meager  data  will  admit.  In  preparing 
his  report  it  seemed  desirable  to  describe  first  the  geographical  distribution 
of  the  various  rock  exposures,  their  lithological  characteristics,  and  their 
strike  and  dip,  without  any  special  reference  to  conclusions  which  might  be 
drawn  from  these  (Chapters  II-VI).  This  seemed  preferable,  since  the 
exposures  furnish  the  basis  for  all  conclusions,  but  the  inferences  drawn 
are  not  always  as  imperative  as  in  the  case  of  other  geological  fields  where 
exposures  are  more  frequent  or  admit  of  more  ready  interpretation.  While, 
therefore,  a  description  of  the  exposures  would  have  permanent  value,  the 
interpretation  of  the  geological  structure  might  vary  with  the  increase  of 
our  knowledge  of  the  geological  data  involved.  Many  localities,  at  present 
still  concealed  by  the  soil,  are  likely  to  be  exposed  in  the  future  by  the 
construction  of  roads  or  the  digging  of  wells,  foundations,  and  sewers. 
The  correlation  of  the  beds  exposed  in  various  parts  of  the  field,  and  the 
conclusions  concerning  their  relative  age,  receive  special  attention  in  the 
later  chapters  of  the  report  (Chapters  VII-XI). 

The  description  of  localities  in  geographical  order  is  begun  in  Chapter 
II  with  Dutch  Island,  the  most  western  locality  in  the  southern  part  of 
Narragansett  Bay  in  which  fossils  have  been  found.  In  going  from  this 
island  to  Fox  Hill  and  the  northern  part  of  Conanicut  we  remain  in  the 
same  series  of  rocks,  and  are  better  prej^ared  to  understand  the  differences, 
stated  later,  between  the  Kingstown  beds  and  the  Aquidneck  shales,  which 
occupy  most  of  the  remainder  of  the  island.  After  this,  Hope  and  Prudence 
islands  ai-e  desci'ibed,  these  islands  being  more  nearly  in  line  of  strike  with 
Conanicut  than  with  other  regions  southward,  and  presenting  rocks  at  least 
of  approximately  similar  horizons. 

MON  XXXIII 15 


226  GEOLOGY  OF  THE  NARRAGANSETT  BASIN. 

Chapter  III  is  devoted  to  a  discussion  of  the  exposures  on  the  western 
side  of  the  bay.  Directly  west  of  Dutch  Island  lies  Saunderstown.  The 
shore  exposures  south  of  this  locality  show  lithologically  all  the  features  of 
the  Carboniferous  of  Dutch  Island  and  northwestern  Conanicut,  so  that, 
although  fossils  are  not  found,  the  geological  position  of  the  beds  is  fairly 
certain.  Southward,  however,  metamorphism  becomes  more  pronounced, 
the  Carboniferous  exposures  are  no  longer  so  continuous,  they  are  separated 
by  large  pegmatite  intrusions,  and  finally  appear  only  as  rare  inclusions 
in  the  pegmatitic  granites  of  Boston  Neck  and  Nai-ragansett  Pier.  The 
gradual  character  of  these  changes  prepares  the  student  for  the  conclusion 
that  even  these  southern  rocks  and  the  Tower  Hill  exposures  are  Carbon- 
iferous. From  this  region  northward  the  Carboniferous  age  of  the  rocks 
must  be  conceded. 

In  Chapter  IV  the  exposures  between  Providence  River  and  Taunton 
River,  on  the  northern  side  of  the  bay,  are  taken  up. 

Following  the  eastern  shore  of  the  bay  southward,  it  is  conveniently 
possible,  first,  to  describe  all  that  is  accurately  known  of  the  Carboniferous 
formation  on  this  shore,  and  then  to  discuss  the  probably  pre-Carboniferous 
rocks  of  Little  Compton.     This  is  done  in  Chapter  V. 

In  the  same  way,  beginning  with  the  basal  arkoses  at  Sachuest  Neck, 
it  is  possible  to  describe  all  the  more  evident  stnictm-es  of  Aquidneck 
Island  before  the  more  doubtful  regions  near  ]\Iiantonomy  Hill,  and  then 
those  toward  Newport  Neck.     This  is  done  in  Chapter  VI. 

It  has  been  the  Avriter's  aim  so  to  arrange  the  materials  as  to  proceed 
from  the  better  known  to  the  less  evident  facts  and  structures. 

The  conclusions  founded  on  these  observations  form  the  basis  of  the 
second  part  of  this  report,  inclnding  Chapters  VII  to  XI,  and  have  been 
placed  toward  the  close.  They  are  necessarily  of  a  more  argumentative 
character,  and  the  attempt  has  been  made  to  bring  out  more  sharply  the 
inferences  deduced  from  the  facts  by  removing  from  this  part  of  the  report 
all  unnecessary  references  to  the  more  minute  details  of  the  geological 
features  presented  by  the  individual  exposures.  It  is  this  part  of  the  report 
which  must  necessarily  be  subject  to  revision,  and  which  nevertheless  is 
the  more  important,  since  it  gives  the  results  of  the  work.  No  one  has  had 
more  occasion  to  regret  the  scantiness  of  continuous  exposures  in  an  east- 
west  direction  in  this  area,  across  the  strike,  than  the  writer,  for  this  has 
left  his  efforts  in  the  field  often  of  little  avail. 


CHAPTER    II. 
THE  WESTERN  ISLANDS  OF  THE  BAY. 

DUTCH   ISLAND. 

From  the  western  side  of  the  island,  nearer  its  northern  end,  a  triangn- 
lar  piece  of  sandy  beach  extends  into  the  western  passage  of  the  bay. 
Southward  from  this  beach  there  is  a  continuous  exposure  of  Carboniferous 
rocks  along  the  shore.  The  more  northern  portion  consists  chiefly  of  black 
shales,  which  sometimes  are  very  coaly.  At  a  point  about  400  feet  south 
of  the  beach  and  directly  west  of  the  largest  building  on  this  shore,  a 
number  of  fern  leaves  were  found  in  the  coaly  shale,  the  shale  being  free 
from  any  marked  signs  of  metamorjDhism,  excepting  the  usual  cleavage. 
The  strike  of  the  shales  is  N.  30°  E.;  dip  eastward,  variable,  but  very  dis- 
tinct, averaging  perhaps  45°.  Sandy  layers  are  more  or  less  frequently 
intercalated  in  the  shales.  Farther  south  there  is  an  alternation  of  sand- 
stone and  conglomerates  with  some  coaly  shales.  The  strike  is  N.  30°  E.; 
the  dip  is  still  eastward.  Along  the  last  1,000  feet  sandstone  prevails. 
Here  is  shown  a  fine  instance  of  crumpled  strata.  The  layers  can  be  well ' 
distinguished,  and  the  flexures  which  they  have  undergone  can  readily 
be  traced.  Notwithstanding  the  flexuring,  the  dip  of  the  sandstone  can 
be  seen  to  be  distinctly  eastward.  The  strike  is  nearly  north  and  south,  or 
slightly  east  of  north.  Near  the  light-house  there  is  not  sufficient  exposure 
to  make  a  determination  of  the  dip.  Along  the  east  shore  northward 
from  the  light-house  the  crumpling  of  the  sandstone  continues.  A  fine 
exposure  of  conglomerate,  forming  a  bed  about  8  feet  thick  and  free 
from  crumpling,  shows  the  dip  to  be  about  50°  E.  The  strike  is  N.  20°  E. 
The  conglomerate  borders  the  western  side  of  an  embayment  about  a  third 
of  the  length  of  the  island  north  of  the  light-house.  The  point  forming 
the  eastern  side  of  the  embayment  consists  again  of  crumpled  sandstone, 
with  a  few  thin  layers  of  conglomerate,  the  dip  being  distinctly  eastward 
as  far  north  as  the  wharf,  a  third  of  the  length  of  the  island  from  its  northern 


228  GEOLOGY  OF  THE  NARRAGAKSETT  BASIN. 

end.  The  same  sandstones  with  thm  conglomerate  layers  are  also  found 
north  of  the  wharf,  as  far  as  the  obtuse  northeast  angle  of  the  shore.  The 
strike  here  is  N.  16°  E.,  and  the  dip  of  the  strata,  as  actually  exposed,  is 
nearly  vertical,  though  a  consideration  of  the  more  southern  exposures  of 
this  series  warrants  the  belief  that  the  general  dip  is  eastward. 

In  general,  the  strata  of  Dutch  Island  may  be  described  as  consisting 
chiefly  of  sandstones  with  subsidiary  conglomerate  layers,  underlain  on  the 
extreme  western  border  by  a  series  in  which  black,  often  coaly,  shales  pre- 
dominate. The  general  strike  is  N.  20°  E.,  becoming  more  directly  north- 
ward at  the  south  end.  The  dip  is  eastward.  A  continuation  of  the  strike 
northward  would  carry  this  sei'ies  to  the  western  side  of  Conanicut,  at  the 
southei'n  end  of  the  line  of  exposures  corresponding  to  Slocums  Ledge. 
Here,  in  fact,  a  similar  series  of  rocks  occurs,  but  the  strike  is  more  north- 
ward (N.  3°  E.);  the  dip  eastward.  Continuing  the  strike  southward,  the 
most  eastern  exposure  on  Dutch  Island  sliould  pass  to  the  west  of  Beaver 
Head  or  Fox  Hill,  the  nearest  part  of  Conanicut.  Yet,  even  if  this  be  the 
case,  there  is  no  doubt  that  the  Fox  Hill  strata  belong  to  the  same  general 
series,  and  if  the}'"  represent  a  higher  horizon  there  is  plenty  of  room  on 
Conanicut  for  the  combined  series. 

The  degree  of  metamorphism  shown  by  the  Dutch  Island  rocks  will 
be  discussed  in  connection  with  the  metamorphism  shown  by  the  corre- 
sponding rocks  on  Conanicut. 

COISTAXICUT  ISLAXD. 

FOX  HILL,  BEAVER   HEAD. 

Sandstone  and  several  conglomerate  layers  are  found  along  the  more 
western  margin  of  the  hill  along  the  shore  as  far  as  its  southwestern  point, 
the  beginning  of  the  beach.  Some  of  the  pebbles  of  the  cong-lomerate  layers 
are  fairly  large,  and  one  or  two  a  little  over  a  foot  in  length  Avere  found. 
The  beds  containing  these  pebbles  can  not  be  compared,  however,  with  the 
Purgatory  conglomerates;  still,  the  presence  of  large  pebbles  is  noteworthy. 
Near  the  southern  end  of  the  series  of  exposures  the  coaly  shales  show 
considerable  crumpling.  This  becomes  less  marked  northward,  where 
the  strike  is  found  to  be  N.  18°  E.,  and  the  dip  as  low  as  30°  E.     Over- 


OONANICUT  ISLAND.  •  229 

lying  the  sandstone  and  conglomerates  along  the  entire  northern  margin  of 
the  hill  is  a  series  of  black  shales,  at  times  very  coaly.  Intercalated  with 
the  shales  were  narrow  bands  of  sandstone,  indicating  a  low  eastward  dip, 
sometimes  as  low  as  20°.  This  eastward  dip  is  significant  in  connection 
with  the  question  of  the  comparative  geological  age  of  the  green  shale 
lying  immediately  to  the  east. 

NORTHERN   HALF  OF  THE  ISLAND,  NORTH   OF  ROUND   SWAMP. 

The  first  exposure  of  rock  on  the  western  shore  occurs  just  south  of  a 
very  small  sand  beach,  where  the  coast  line  of  the  island  begins  to  take 
a  direct  northern  course.  Here  occurs  sandstone  witli  some  thin  conglom- 
erate layers  showing  a  strike  of  N.  5°  E.  and  an  eastward  dip.  North  of 
the  beach  there  is  a  stretch  of  coaly  shale,  with  an  eastward  dip.  Then 
follows  northward  a  series  of  sandstones  with  interbedded  conglomerate 
layers,  as  far  as  a  small  stream  entering  the  bay  near  the  north  end  of 
Slocums  Ledge.  Northward  coaly  shale  is  again  exjDOsed,  showing  a  strike 
of  N.  8°  E.  and  an  eastward  dip.  Yet  north  of  this  is  a  long  sandstone 
exposure  with  a  strike  of  N.  13°  E.  and  an  eastward  dip.  Still  farther  north 
occur  coaly  shales  again,  as  far  as  Fowler  Rock,  near  the  middle  of  Great 
Ledge.  The  line  of  shore  exposures  above  mentioned,  which  might  be 
called  the  ledge  exposures  on  account  of  their  proximity  to  Slocums  and 
Great  ledges,  show  the  greatest  degree  of  metamorphism  among  the  rocks 
of  the  island.  From  Fowler  Rock  to  a  short  distance  northeast  of  Sand 
Point  there  are  no  shore  exposures. 

Northeast  of  Sand  Point  the  shore  lies  on  coaly  shales  interstratified 
with  sandstones.  The  strike  is  N.  3°  E.;  the  dip  is  also  east.  Northward 
there  are  sandstones  with  minor  conglomerate  layers,  having  the  same  sti'ike. 
Farther  north  is  more  coaly  shale,  with  intercalated  sandstones,  with  the 
same  strike  of  N.  3°  E.,  and  this  is  also  shown  by  the  most  northei-n 
exposures  on  the  western  side  of  the  island,  coaly  shales  being  exposed  just 
west  of  North  Point. 

Exposures  begin  again  about  1,200  feet  east  of  North  Point  along  the 
north  shore  and  continue  for  several  hundred  feet.  The  rocks  are  chiefly 
shales,  much  squeezed  in  a  direction  from  east  to  west,  making  a  strike  of 
N.  18°  E.  and  an  uncertain  dip,  which  is  believed,  however,  to  be  eastward. 
The  next  exposures  along  the  eastern  shore,  going  south,  are  almost  directly 


230  GEOLOGY  OF  THE  NARRAGANSETT  BASIN. 

east  of  Sand  Point,  wliich  lies  on  the  ^-estern  shore.  Here  are  found  gray 
sandstones  and  shales,  with  a  strike  of  N.  8°  E.  and  a  vertical  dip.  In  a 
small  embayment  to  the  sonth,  almost  east  of  the  crest  of  the  unnamed 
100-foot  hill  indicated  on  the  map,  is  black  shale,  often  coaly.  In  one 
of  the  coaly  shale  layers  in  the  most  indented  jDart  of  this  embayment, 
fossil  fern  leaves  are  not  imcommon.  The  strike  is  N.  13°  E.  and  the  dip 
vertical.  South  of  this  embayment  occurs  a  line  of  sandstone,  with  a 
strike  of  N.  13°  E.  and  a  dip  which  is  almost  vertical,  but  slightly  inclined 
toward  the  west;  but  there  are  very  low  dips  in  various  directions  farther 
south,  indicating  crumpling  and  folding  in  the  rock.  As  the  shore  begins 
to  curve  toward  the  SSE.  exposures  are  wanting,  but  farther  south  there 
is  a  grayish  sandstone  striking  N.-S.,  with  a  dip  of  70°  to  80°  E.,  toward 
the  southwest  of  which  is  a  dark  shale,  and  farther  southwest  occurs  a  black 
coaly  shale  with  a  strike  N.  9°  E.  For  some  distance  southward  there  is  an 
absence  of  exposures.  Farther  south,  past  the  mouth  of  a  little  stream  enter- 
ing the  bay,  inore  of  the  coaly  shale  occurs,  in  the  most  western  portion 
of  this  long  embayment.  A  short  distance  south  of  a  point  directly  west  of 
the  southern  end  of  Gould  Island  black  shales  occur,  with  irregular  dip  and 
strike,  indicating  crumpling  of  strata.  It  is  near  the  old  feny,  and  is  the 
most  southern  of  this  series  of  rocks  on  the  east  shore. 

A  line  connecting  the  small  embayment  immediately  south  of  the  old 
ferry  with  the  pond  east  of  Fox  Hill  would  indicate  approximately  the 
eastern  limit  of  the  Kingstown  sandstones  with  conglomerates  and  the  coaly 
shales.  South  and  east  of  this  line  lies  the  great  Conanicut  shale  series, 
which  is  a  part  of  the  Aquidneck  shale  series,  hereafter  to  be  described. 

The  strike  of  both  the  eastern  and  the  western  portion  of  the  exposures 
in  northern  Conanicut  averages  about  N.  8°  E.  Along  the  western  shore 
there  is  no  marked  crumpling,  and  the  dip  is  distinctly  east,  averaging 
perhaps  40°  to  50°.  On  the  eastern  side  the  dips  are  frequently  vertical, 
and  sometimes  horizontal,  as  though  considerable  folding  and  crumpling 
would  be  shown  if  there  were  any  long  vertical  sections  across  the  strike 

The  western  portion  of  the  northern  half  of  the  island  shows  consid- 
erably more  metamorphism  than  the  eastern  portion,  and  the  most  meta- 
morphosed portion  is  that  bordering  the  shore  along  Slocums  and  Great 
ledofes. 


GOlSrANICUT  ISLAND.  231 

Here  the  pebbles  of  the  conglomerates  have  been  squeezed  into  thm 
sheets,  often  several  inches  long'  and  hardly  more  than  a  quarter  of  an 
inch  in  thickness,  so  that  it  is  difficult  at  times  to  recognize  the  conglom- 
eratic nature  of  a  layer  if  seen  in  a  section  transverse  to  the  cleavage,  while 
along  the  plane  of  shearing  the  pebbles  are  very  easily  recognized.  This 
flattening  of  the  pebbles  is  shown  to  an  equal  degree  in  the  conglomerate 
at  the  western  base  of  Fox  Hill,  on  Dutch  Island,  and  along  the  more 
northern  and  eastern  exposures  on  Conanicut. 

The  sandstones  and  shales  exposed  along  the  shore  at  Slocums  and 
Great  ledges  frequently  contain  garnets.  These  are  of  much  larger  size 
than  any  found  farther  north  on  the  island.  Grarnets  in  the  sandstones  on 
the  eastern  side  of  Conanicut  are  very  small,  and  those  in  the  shales  are 
yet  smaller.' 

A  walk  around  the  border  of  the  island  is  very  instructive.  The  most 
eastern  coaly  shale  exposures  are,  except  for  their  cleavage,  but  little  affected 
by  metamorphism,  and  for  this  reason  it  was  not  difficult  to  find  fossil  ferns 
there,  while  along  the  ledge  exposures  on  the  west  the  frequency  of  large 
garnets,  and  often  also  of  staurolites,  makes  the  detection  of  fossil  ferns  in 
these  shales  very  difficult.  Nevertheless,  Prof  T.  Nelson  Dale  found  a 
number  of  well-preserved  fossil  ferns  somewhere  along  the  ledge  exposures, 
in  a  layer  of  black  coal}^  shale,  hardly  more  than  a  foot  thick,  included 
between  shales  containing  staurolite,  garnets,  and  ottrelite. 

Staurolite  was  found  only  along  the  cliff  exposui-es,  but  in  places  it 
was  very  abundant.  It  was  not  seen  on  Dutch  Island  or  Fox  Hill.  Garnets 
were  found  in  the  shales  on  Dutch  Island,  but  in  some  of  the  shales  they 
were  entirely  absent.  In  the  black  and  coaly  shales  at  Fox  Hill  they  were 
rare,  although  occurring  in  great  numbers  in  the  overlying  green  schists 
south  of  Fox  Hill.  At  several  localities  on  Conanicut  and  Dutch  islands 
radiate  aggregates  of  a  greenish  mineral  are  found  rather  abundantly  in 
this  series  of  rocks.  These  aggregates  are  instructive  in  connection  with 
the  exposures  on  Gould  Island,  in  the  northern  part  of  Sakonnet  River. 
While  the  metamorphism  undoubtedly  increased  in  intensity  westward,  in 
this  region  it  did  not  increase  regularly  so  as  to  make  Fox  Hill  and  Dutch 
Island  show  more  metamorphism  than  the  cliff  exposures  of  Conanicut. 

'  On  metamorphism  in  the  Rhode  Island  coal  basin,  by  T.  Nelson  Dale:  Proc.  Newport  Nat. 
Hist.  Soc,  Doc.  3,  1885,  pp.  85-86. 


232  GEOLOGY  OF  THE  NARRAGANSBTT  BASIN. 

SOUTHERN    HALF   OF   THE   ISLAND,   SOUTH    OF   ROUND    SWAMP. 
SHALE   REGION. 

The  most  northern  outcrop  of  the  Conanicut  shales  is  in  a  small 
embayment  north  of  Potters  Cove,  about  1,800  feet  south  of  the  old  ferry. 
They  are  here  very  thin  and  fissile.  They  are  again  exposed  for  quite  a 
long  distance  along  the  northern  part  of  Potters  Cove.  At  its  southern 
extremitv,  and  thence  all  around  the  margin  of  Freebodys  Hill  and  beyond 
Jamestown  Ferry,  there  is  an  almost  continuous  exposure,  the  outcrops 
ceasing  about  half  a  mile  south  of  the  ferry  point.  At  Taylors  Point  the 
shale  contains  quartzitic  layers.  If  these  are  original  interstratified  sandstone 
layers  there  has  been  much  lateral  crumpling.  Nevertheless,  the  beds  show 
a  generally  low  dip.  Along  the  eastern  shore  of  Freebodys  Hill  there  is 
distinct  color  banding,  accompanied  by  considerable  crumpling.  The  most 
northern  of  the  outcrops  of  the  shales  along  the  western  shore  lies  within 
half  a  mile  north  of  the  western  Jamestown  ferry.  Thence  outcrops  occur 
at  more  or  less  frequent  intervals  as  far  as  the  marshy  land,  a  short  distance 
south  of  the  western  ferry;  then,  after  a  short  interval,  along  the  eastern 
shore  of  Mackerel  Cove.  Shales  occur  again  a  third  of  a  mile  south  of  the 
western  ferry,  along  the  southern  margin  of  Dutch  Island  Harbor,  on  the 
northern  edge  of  tlie  southern  half  of  Conanicut,  east  of  the  pond  near 
Fox  Hill.  South  of  Fox  Hill  they  occur  again  at  the  end  of  a  beach  about 
a  sixth  of  a  mile  long.  Here  they  are  very  glistening  and  are  filled  with 
some  ferruginous  mineral,  not  closely  examined  in  the  field,  but  probably 
pyrite.  Thence  the  same  shales  are  found  around  the  entire  margin  of  this 
part  of  the  island,  around  Beaver  Tail  Head,  thence  northward  into  Mack- 
erel Cove  to  its  northern  extremity,  and  thence  from  the  eastern  end  of  the 
sand  bar  connecting  the  two  parts  of  the  island,  down  the  eastern  side  of 
the  cove,  to  a  point  where  a  small  stream  enters  the  cove. 

Two  minette  dikes  cut  the  Conanicut  shales  in  the  southern  half  of 
the  island.  One  dike  extends  from  the  northern  side  of  Hulls  Cove  to  the 
northern  edge  of  Austins  PIollow ;  the  other  extends  from  Lions  Head  to 
the  Southern  edge  of  Austins  Hollow. 

The  color  of  the  Conanicut  shales  is  somewhat  variable.  Where  dry 
and  long  exposed  to  the  action  of  weathering  they  are  lighter  in  color, 
verging  toward  greenish,  with  a  tint  of  blue  or  brown;  where  wet  they 


CONANICUT  ISLAND.  233 

are  darker  in  color,  usually  dark  blue,  often  almost  black,  but  not  of  the 
dense  black  hue  characteristic  of  the  shales  often  called  coaly  in  this  paper, 
in  which  fossil  ferns  are  usually  present.  These  shades  of  color  are  also 
found  where  they  are  not  due  to  variations  of  moisture,  but  in  general  the 
dark-blue  type  prevails,  excepting-  in  the  more  weathered  portions.  Dark 
color  banding  not  infrequently  indicates  the  true  dip  and  strike.  While  the 
general  strike  is  undoubtedly  northerly,  the  dip  is  not  so  easy  to  determine. 
While  the  writer  believes  that  the  series  of  shales  as  a  whole  overlies 
the  series  of  sandstones,  conglomerates,  and  coaly  shales  already  described, 
and  while  an  easterly  dip  would  best  accord  with  such  belief,  it  is  only 
proper  to  mention  that  the  time  at  his  disposal  did  not  enable  him  to  make 
a  satisfactory  study  of  the  problem.  The  dips  on  the  western  side  of  the 
shale  series  were  often  found  to  be  very  steep,  almost  vertical,  and  in  some 
very  large  exposures  more  or  less  steep  westward,  while  on  the  eastern 
side,  as  far  as  the  northern  part  of  Mackerel  Cove,  the  dips  were  less  vertical 
and  were  often  eastward.  The  chief  reason  for  believing  that  the  Conanicut 
shales  are  above  the  Kingstown  sandstone  conglomerate  and  coaly  shale 
series  is  their  occurrence  east  of  the  latter,  especially  east  of  Fox  Hill,  and 
the  uniform  eastward  dips  of  the  latter  series,  especially  at  Fox  Hill,  but 
also  on  Dutch  Island.  Unfortunately,  the  uniform  east  dip  along  the  western 
margin  of  northern  Conanicut  is  not  continued  in  an  equally  ajDparent  man- 
ner in  the  more  crumpled  and  folded  series  on  the  eastern  side  of  the  island. 

GRANITE  AREA,  THE  DUMPLINGS,  AND  ARKOSE  REGION  WEST  OF  THE  DUMPLINGS. 

Coarse  granite,  in  part  filled  with  large  phenocrysts  of  orthoclase,  occu- 
pies the  southern  end  of  the  northeastern  half  of  Conanicut,  from  the 
southern  side  of  Bulls  Point  to  Mackerel  Cove.  North  of  the  granite,  on 
the  Mackerel  Cove  side,  is  a  considerable  exposure  of  arkose.  Near  the 
granite  the  arkose  contains  some  of  the  large  phenocrysts  of  orthoclase 
derived  from  the  granite,  scarcely  broken  up.  Farther  from  the  granite  the 
large  phenocrysts  are  more  rare.  Interbedded  with  the  arkose  are  more 
carbonaceous,  sandy,  and  shaly  layers,  with  strike  about  N.  70°  E.  near 
the  granite.  The  arkose  is  exposed  along  Mackerel  Cove  as  far  as  a  little 
stream  entering  the  cove  from  the  east.  North  of  the  mouth  of  this  stream 
only  the  Conanicut  shale  series  is  exposed.     The  color  banding  of  this  shale 


234  GEOLOGY  OF  THE  NARKAGANSETT  BASIISr. 

is  at  several  points  very  distinct,  and  a  careful  examination  of  the  same  seems 
to  indicate  that  the  shales  strike  more  nearly  north-south,  and  dip  at  a  low 
angle  eastward.  The  stream  indicates  a  line  of  fault  between  the  shales 
and  the  arkose  beds. 

The  relative  age  of  the  arkose  beds  and  of  the  green  Conanicut  shales 
is  not  known.  The  arkose  beds  are  undoubtedly  Carboniferous.  They 
give  evidence  of  interbedded  layers  of  somewhat  carbonaceous  shales. 
Some  of  these  shale  layers  were  thin,  and  suffered  enough  erosion  from  the 
variable  ciirrents  present  during  the  deposition  of  the  grit  to  cause  the 
remnants  of  the  shale  layers  to  appear  like  fragments  of  shale  inclosed  in 
certain  courses  of  the  grit.  The  green  Conanicut  shales  are  also  Carbonif- 
erous. But  there  is  no  gradation  of  the  grit  into  the  Conanicut  shale 
immediately  to  the  north.  Those  parts  of  the  arkose  and  of  the  Conanicut 
shales  actually  exposed  along  Mackerel  Cove  are  therefore  not  .strictly  of 
the  same  age,  although  both  are  of  Carboniferous  age.  A  line  of  fault 
separates  them.  Since  neither  the  upthrow  nor  the  downthrow  of  the  fault 
is  known,  it  is  impossible  to  determine  by  comparison  of  their  exposure 
which  is  the  older. 

Nortli  of  the  eastern  half  of  the  granite  area  is  found  a  greenish  rock, 
here  called  the  Dumpling  rock.  In  places,  especially  in  the  northern  out- 
crops along  the  shore,  it  is  purplish,  looks  very  much  like  an  argillite,  and 
seems  to  show  genuine  stratification.  Farther  south  along  the  shore,  at  a 
promontory,  it  seems  to  contain  pebbles.  Still  farther  south,  however,  and 
along  all  the  inland  exposures,  from  the  eastern  side  of  Conanicut,  along 
the  northern  margin  of  the  granite  area,  toward  the  cove,  the  Dumpling 
rock  is  greenish  in  color,  fine  grained,  of  homogeneous  texture,  gives  no 
evidence  of  clastic  origin,  is  cracked  in  all  directions,  and  does  not  have 
the  appearance  of  a  stratified  rock.  It  bears  a  strong  resemblance  to  the 
greenish  rock  found  along  the  southern  Newport  Cliffs  south  of  Sheep 
Point.  To  a  less  degree  it  resembles  the  greenish  and  purplish  rock  form- 
ing the  middle  third  of  Newport  Neck.  The  most  northern  outcrop  of 
this  greenish  rock  is  along  the  shore  half  a  mile  south  of  Jamestown 
Ferry.  Thence  it  extends  inland  for  half  a  mile  in  a  southwest  direction. 
Here  the  northern  boundary  seems  to  meet  the  southern  in  a  sharp  angle 
(see  map,  PL  XXXI).  The  gi-anite  area  lies  but  a  short  distance  southward, 
and  the  northern  border  of  the  granite  passes  irregularly  eastward,  south  of 
the  Dumpling  rock  area,  at  first  about  N.  70°  E.,  then  S.  70°  E.  to  the 


HOPE  ISLAND.  235 

shore  a  third  of  a  mile  northwest  of  Bulls  Point,  then  reappearing  on  the 
promontory  of  Bulls  Point,  forming  the  northeast  shore  of  the  promontory 
to  its  extremity.  The  southern  part  of  the  rock  island  southeast  of  Bulls 
Point  is  granite.  All  the  rock  islands  north  and  northeast  of  Bulls  Point, 
including  the  Dumplings,  are  foi-med  by  the  greenish  Dumpling  rock.  This 
Dumpling  rock  is  older  than  the  granite.  This  is  shown  by  the  fine-granied 
structure  of  the  granite  wherever  it  comes  in  contact  with  the  Dumpling 
rock.  The  greenish  Dumpling  rock  along  a  road  near  the  contact  half  a 
mile  northwest  of  Bulls  Point,  and  along  the  point  itself,  is  penetrated  by 
dikes  of  pink  or  reddish  aplites  of  rather  fine  grain.  This  aplite  is  still 
more  common  in  the  granite  area,  and  evidently  represents  a  later  intru- 
sion, after  the  great  granite  mass  had  cooled  considerably.  Sometimes  the 
aplite  is  rather  coarse,  biit  never  so  coarse  as  the  granite  mass  itself.  The 
Dumpling  rock  is  considered  an  argillite,  formed  by  the  raetaphoric  action 
of  pre-Carbonifei'Ous  granite  on  still  earlier,  ^Jossibly  Cambrian,  shaly  rock. 
At  no  point  does  the  greenish  Dumpling  rock  of  Conanicut  come  in 
contact  with  the  Conanicut  shale  series  at  the  surface.  The  Clearest  points 
of  approach  are  at  least  several  hundred  yards  distant.  The  arkose  may 
once  have  extended  along  the  northern  part  of  the  greenish  Dumpling  rock 
toward  northern  Rose  Island  and  southern  Coasters  Harbor  Island.  There 
is  certainly  a  great  temptation  to  assume  the  existence  of  an  island^  in  Car- 
boniferous times,  consisting  of  granite,  Dumpling  rock,  and  the  Brenton 
Point  shales.  This  island  would  include  the  Newport  Harbor  Islands  south 
of  the  line  above  mentioned,  the  area  east  of  southern  Mackerel  Cove  on 
Conanicut,  and  Newport  Neck.  Kettlebottom  Rock,  a  short  distance  south 
of  the  southwestern  end  of  the  granite  area,  consists  of  Conanicut  shale. 

HOPE  ISLAND. 

The  pier  is  at  a  pi'ojection  about  900  feet  south  of  the  northeast  angle 
of  the  island.  From  the  em.bayment  on  the  eastern  side  of  the  island  south 
of  the  pier  to  a  similar  indentation  on  the  western  shore  an  east-west 
fault  seems  to  run.  The  beds  both  north  and  south  of  the  pier  seem  to 
have  very  steep  dips,  with  variable  strike.  At  the  northeastern  angle  of  the 
island,  however,  they  dip  at  a  low  angle  northeastward.  The  rock  at  this 
end  is  a  white  quartzitic  sandstone  with  few    pebble   layers.     Westward 

'  T.  Nelson  Dale :  Ara.  Jour.  Sci.,  3cl  series,  Vol.  XXVII,  1884,  pp.  217-228,  282-289,  map. 


236  GEOLOGY  OF  THE  NAERAGANSETT  BASIN, 

along  the  northern  margin  of  the  island  black  shales  and  fine-grained  sand- 
stones underlie  the  sandstone,  dipping  northeastward.  Farther  west,  extend- 
ing from  the  northwest  angle  of  the  island  to  the  indentation  northwest  of 
the  dwelling  house,  is  more  white  quartzitic  sandstone,  dipping  under  the 
black  shales  at  a  low  angle  to  the  northeast.  Near  the  southern  end  of 
this  part  of  the  shore  a  black  shale  layer  is  seen  to  underlie  the  sandstone. 

South  of  the  fault  line,  on  the  west  shore,  are  found  in  succession  the 
following  rocks,  numbered  downward  in  the  section  : 

(1)  Black  shaly  rock,  strike  N.  30°  E.,  dip  80°  E.,  the  strike  continu- 
ing far  southward. 

(2)  Conglomerate  with  small  pebbles  and  with  flakes  of  black  shales 
in  the  lower  courses. 

(3)  Black  shale. 

(4)  A  considerable  thickness  of  sandstone,  becoming  conglomeratic 
southward  along  the  strike;  dip  about  vertical,  becoming  60°  W.,  then  45° 
W.,  then  more  nearly  vertical,  and  finally,  on  going  southward,  70°  E. 
again. 

(5)  Black  shales  adjoin  the  sandstone  on  the  west.  This  black  shale 
layer  makes  its  appearance  in  the  projection  southeast  of  Gooseberry  Island 
and  continues  to  be  exposed  or  otherwise  indicated  for  a  distance  of  1,000 
feet.     The  strike  is  parallel  to  the  shore,  and  the  dip  is  70°  to  60°  E. 

(6)  West  of  this  black  shale  layer  occurs  sandstone,  more  black  shale, 
and  again  sandstone  on  the  shore  southeast  of  Seal  Rocks. 

(7)  East  of  this  long  black  shale  layer  occurs  a  great  mass  of  sand- 
stone as  far  as  the  south  end  of  the  island,  becoming  conglomeratic  along 
the  eastern  side  of  the  island,  being  there  often  a  rapid  altei'uation  of  sand- 
stone and  conglomerate  layers.  Along  the  eastern  side  of  Hojje  Island  the 
dips  are  low  eastward,  usually  30°  to  45°. 

The  sandstones  of  Hope  Island  are  very  white  and  quartzitic,  but  abun- 
dantly specked  by  some  small  black  micaceous  mineral,  probably  biotite. 
The  blue  and  gray  color  ot  the  standstones,  so  characteristic  in  less  meta- 
morphosed regions,  has  disappeared.  Pebbles  are  present  to  a  certain  meas- 
ure ill  all  the  sandstone  layers,  but  on  the  western  side  of  the  island  the 
sandstone  predominates  greatly,  while  along  the  eastern  shore  almost  half 
of  the  rock  is  conglomeratic.  The  black  shaly  and  evidently  Carboniferous 
beds  are  found  only  along  the  western  and  northern  shore,  and  evidently  form 


PRUDKNOE  ISLAND.  237 

the  lower  beds  of  the  small  section  here  exposed.  These  shales  are  every- 
where filled  with  dark  minerals,  which  in  some  cases  resemble,  macroscop- 
ically,  ottrelite,  and  in  other  cases  may  be  some  other  dark  micaceous 
mineral.  The  pebbles  of  the  conglomerate  are  uniformly  small,  usually 
not  over  li  inches  in  diameter.  Many  of  them  are  distinctly  quartzitic  or 
granitic;  in  the  latter  case  of  medium  grain,  of  bluish  tint,  and  without 
phenocrysts. 

There  has  been  no  flattening  of  pebbles  or  considerable  shearing, 
metamorphism  being,  however,  abundantly  shown  by  the  frequent  presence 
cf  black  mica  in  the  sandstone  and  of  ottrelite  in  the  black  shales. 

A  continuation  of  the  strikes  along  the  entire  Avestern  margin  of 
Conanicut  would  carry  the  series  there  exposed  to  Hope  Island.  The 
form  of  the  sea  bottom  between  these  two  islands  also  suggests  a  general 
continuity  of  strata,  and  the  rocks  exposed  on  Hope  Island  are  believed 
to  belong  to  the  same  general  series  as  those  exposed  on  Conanicut,  although 
possibly  just  beneath  that  series,  as  is  indicated  by  the  more  quartzitic 
phase  and  the  general  absence  of  the  more  argillaceous  or  slaty  pebbles, 
the  latter  being  more  frequently  quartzitic  and  granitic.  At  Hope  Island, 
however,  the  strikes  are  much  more  toward  the  northeast,  averaging  N.  30°E. 

A  continuation  of  the  strike  would  carry  these  rocks  toward  Johnsons 
and  Pine  Hill  ledges  south  of  Pine  Hill  Point,  on  the  western  shore  of 
Prudence  Island.     Whether  they  occur  there  could  not  be  determined. 

PRUDEINCE  ISLAND. 

The  lowest  rocks  exposed  on  the  west  side  of  the  island  are  found 
north  of  Prudence  Park  wharf,  and  continue  thence  northward,  forming 
the  shore  for  a  little  over  a  mile,  with  an  average  strike  of  N.  20°  E. 
and  a  dip  of  25°  to  45°,  at  one  place  60°  E.  The  average  dip  is  about 
35°.  At  the  wharf  the  sand.stone  is  bluish,  with  a  few  thin  conglomerate 
layers.  The  pebbles  are  elongated,  but  much  less  than  at  Hope  Island, 
and  the  general  metamorphism  is  evidently  less.  The  sandstone  series 
appears  again  about  a  quarter  of  a  mile  northward,  at  the  end  of  a  long 
inward  curve  of  the  shore,  where  it  contains  thin  conglomerate  layers. 
Thence  it  follows  the  shore  northward,  the  shale  series  often  appearing  in 
contact  with  the  sandstones  on  the  eastei'u  line  of  outcrop,  on  the  top  of 
the  bank.     Black  carbonaceous  streaks  often  band  the  sandstones.     At  some 


238  GEOLOGY  OF  THE  NARRAGANSETT  BASIN. 

points  the  cross  bedding  is  well  marked.  Thin  but  elongated  pockets  of 
ottrelitic  coaly  shale  are  found  in  places  not  far  northward.  Within  2,700 
feet  of  the  wharf  scattered  pebbles,  sometimes  3.^  inches  long,  not  at  all 
flattened,  occur  in  the  sandstone.  In  a  few  of  these  pebbles  oboli  were 
found.  The  oboli  occur  again  northward  in  a  thin  layer  of  conglom- 
erate, the  pebbles  of  which  are  sometimes  1^  inches  long.  The  oboli  are 
found  once  again,  about  700  feet  north  of  the  first-mentioned  locality, 
in  pebbles  scattered  through  the  sandstone.  The  gray  sandstone  is  not 
infrequently  banded  with  more  carbonaceous  layers.  Farther  north  long, 
thin  fragments  of  carbonaceous  shale  occur  in  small  conglomerate  layers. 
A  little  more  than  three-quarters  of  a  mile  from  the  wharf  the  flattened 
leaf-like  plant  remains  occur,  such  as  are  found  at  Hills  Grove,  Warwick, 
and  Silver  Springs,  East  Providence.  The  outcrops  along  the  shore  cease 
about  a  mile  north  of  the  wharf.  Northeastward  of  this,  in  the  field,  a 
sandy  outcrop,  probably  belonging  in  the  next  higher  series,  occurs.  In 
general,  the  series  here  described  is  composed  of  sandstones.  The  absence 
of  coaly  shale  layers  in  it  does  not  signify  much,  since  the  vertical  section 
here  exposed  probably  does  not  exceed  50  feet. 

The  occurrence  of  a  shaly  series  over  that  of  sandstones  all  along  the 
line  of  outcrop  has  already  been  noticed.  This  shale  series  is  well  exposed 
along  the  long  inward  curve  of  shore  north  of  the  wharf  The  lower 
courses  immediately  over  the  sandstone  look  very  much  like  the  dark-blue 
shales  of  the  Conanicut  series,  but  frequently  contain  ottrelite  and  are 
banded  with  more  frequent  and  much  larger  layers  of  a  very  fine  grained 
sandstone,  which  has  been  less  affected  by  shearing.  Above  these  beds 
occur  decidedly  coaly  shales,  often  siliceous  from  the  presence  of  minute 
clastic  quartz  grains.  Above  these  again  occur  the  fissile  dark-blue  shales. 
The  color  banding  of  the  shales  is  often  very  well  shown,  and  since  there 
has  been  no  crumpling,  or  violent  folding,  it  indicates  the  strike  and  dip  very 
well.  The  strike  averages  N.  20°  E.,  and  the  dip  is  about  35°  E.  The  upper 
dark -blue  fissile  shales  are  exposed  at  a  number  of  points  halfway  up  the 
hillside  east  of  the  wharf  The  very  coaly  black  shales  form  the  shore 
south  of  the  wharf  for  a  distance  of  over  a  mile.  It  must  not  be  imagined 
from  this  that  the  coaly  shales  are  perfectly  distinct  from  the  dark-blue 
members;  on  the  contrary,  they  are  interbedded  with  the  dark-blue  shales 
at  various  levels,  but  nowhere  else  in  the  series  is  so  much  coaly  sliale 


PRUDENCE  ISLAND.  239 

found  as  at  this  level.  The  general  strike  is  parallel  to  the  shore,  about 
N.  10°  E.  south  of  the  wharf,  and  N.  3°  to  5°  E.  farther  south.  The  dip, 
which  is  25°  E.  for  the  g-reater  part  of  the  shore  exposure,  becomes  40°  E. 
near  the  southern  end.  Here  there  is  also  much  local  crumpling,  which 
brings  the  color  bands  of  the  rocks  often  to  a  vertical  position.  The 
crumpling  takes  place  in  a  direction  N.  60°  E. 

South  of  the  wharf  the  coaly  shale  often  shows  distinct  color  banding. 
Gray,  rather  coarse  sandstone  occurs  along  the  top  of  the  cliff.  The  shale 
is  frequently  ottrelitic  About  3,375  feet  south  of  the  wharf  fossil  ferns 
were  found  in  the  coaly  shales,  where  finest  gi'ained  and  least  ottrelitic. 
Ferns  are  difficult  to  find  in  this  series.  It  is  best  to  take  each  slab  of  shale 
in  the  hand  and  hold  it  so  that  the  sunlight  will  bring  out  in  sharper  relief 
all  the  unevenness  of  the  surface.  When  the  fern-leaf  impressions  are  once 
found,  the  character  is  readily  enough  recognized.  In  the  sandstone  which 
occurs  in  the  coaly  shale  series  at  this  point  was  found  the  impression  of  a 
very  large  calamite.  The  longitudinal  ribs  were  very  coarse  and  distinct, 
and  although  the  specimen  was  about  14  inches  long  and  4.^  broad,  yet  it 
showed  not  a  single  joint. 

The  most  northern  exposure  on  the  east  side  of  the  island  occurs  about 
two-thirds  of  a  mile  north  of  the  light-liouse  at  Sand  Point.  Here  is  found 
a  rock  belonging  to  the  shale  series,  finely  color-banded,  very  micaceous, 
but  not  fissile.  The  strike  is  N.  12°  W.  and  the  dip  75°  W.  The  next 
exposure  is  hardly  half  a  mile  north  of  the  light-house.  It  is  very  dark- 
blue  ottrelitic  rock,  belonging  to  the  shale  series.  Its  strike  is  about  N. 
4°  W.  and  its  dip  about  80°  W.  From  the  south  side  of  the  light-house 
southward  for  a  distance  of  1^  miles  there  is  a  continuous  exposui-e  of  the 
shale  series  along  the  shore,  after  which  Ithere  are  several  more  isolated 
exposures  for  about  a  quarter  of  a  mile  farther.  The  rocks  on  this  side 
also  belong  to  the  shale  series,  although  evidently  higher  than  the  basal 
part  of  that  series  as  exposed  on  the  west  shore,  since  neither  the  sand- 
stone-conglomerate series  below  nor  the  lower  black  coaly  shale  layei's  are 
here  exposed.  These  shales  usually  appear  so  different  from  the  Conanicut 
shales  that  at  first  sight  their  close  similarity  might  not  be  recognized,  jet 
careful  observation  will  show  at  once  the  same  sericitic  micaceous  structure. 
The  rock  is  usually  rather  firm,  but  frequently  the  shaly  structure  is  more 
developed  and  then  the  rock  resembles  in  every  particular  the  greenish  and 


240  GEOLOGY  OP  THE  NARRAGANSETT  BASIN. 

the  clark-bluish  shales  of  Conanicut.  The  color  banding  is  iisually  very  pro- 
nounced, and  since  the  contortion  and  folding  of  strata  is  less,  the  general 
strike  and  dip  of  the  rocks  can  be  readily  determined.  These  shaly  rocks 
differ  considerably  from  the  Conanicut  shales,  however,  in  the  more  fre- 
quent presence  of  sandy  courses,  varying  from  1  inch  to  8,  12,  and  even  20 
inches  in  thickness.  These  have  usually  been  less  affected  by  cleavage. 
There  are  also  distinctly  conglomeratic  beds  present,  although  these,  except 
in  the  case  of  two  beds,  occur  only  in  very  thin  layers.  Darker,  more 
coaly  phases  are  present  in  the  shales,  more  carbonaceous  than  any 
observed  on  Conanicut.  The  general  color  of  the  shales  on  the  shore, 
where  not  moistened  by  water,  is  often,  for  rather  long  stretches,  a  peculiar 
silvery  green,  which  resembles  some  phases  of  the  greenish  shales  at  Eas- 
tons  Point.  The  darker  shales  are  frequently  ottrelitic.  Notwithstanding- 
all  these  differences,  a  person  acquainted  with  the  varying  aspect  of  this 
series  will  readily  satisfy  himself  as  to  its  identity  with  the  Conanicut  shales. 

The  general  strike  for  a  distance  south  of  the  wharf  is  N.  10°  E.,  dip 
70°  W.  About  five-sixths  of  a  mile  south  of  the  light-house  the  shale  is 
darker,  more  carbonaceous,  and  ottrelitic.  Farther  south  thin  conglom- 
erate beds  show  stretched  pebbles,  usually  not  exceeding  half  an  inch  in 
leno-th.  Yet  farther  to  the  south  more  carbonaceous  black  shales  occur  close 
to  the  inward  curve  along  the  shore.  Farther  on  there  is  conglomerate 
with  pebbles  an  inch  long,  and  a  little  over  a  mile  south  of  the  light-house 
a  3-foot  layer  of  conglomerate  is  found  with  pebbles  often  3^  inches  long. 
The  pebbles  are  usually  greenish,  as  though  lithologically  similar  to  the 
shales;  they  are  rarely  quartzitic.  Still  farther  southward  more  ottrelitic 
dark  shale  is  seen.  Fine  color  banding  is  often  shown.  Cross  bedding  is 
common  iu  the  coarser  sandstones.  Thin  conglomeratic  layers  begin  to 
be  more  frequent.  Near  this  point  the  continuous  exposures  cease.  At  the 
southern  end  of  these  exposures  the  strike  is  N.  20°  E.,  the  dip  still  70°  to 
80°  W. 

At  the  next  exposure  southward  there  occurs  a  more  carbonaceous 
form  of  the  shale,  black  and  ottrelitic.  Strike  N.  28°  E.,  dip  60°  to  70° 
W.  The  next  exposure,  more  greenish,  gives  again  strike  N.  13°  E.,  dip 
88°  W.  Banded,  slightly  ottrehtic  shales  form  the  last  exposure,  1|  miles 
south  of  the  hght-house ;  strike  N.  33°  E.,  dip  80°  W. 


PECTDENOE  ISLAND.  241 

Potters  Hotel  is  located  two-fifths  of  a  mile  directly  west  of  the  light- 
house. Southeast  of  the  hotel,  in  the  fields,  at  several  localities,  some  of 
them  halfway  down  the  hillside,  occur  fairly  coarse  sandy  layers,  some- 
times slightly  conglomeratic,  accompanying  the  dark-blue  shales.  They 
represent  higher  horizons  in  the  shale  series,  and  form  the  highest  land 
surface  on  the  island.     Their  strike  is  about  N.  10°  E.,  the  dip  80°  W. 

The  strike  on  both  sides  of  the  island,  in  the  section  crossing  near 
Potters  Hotel,  is  approximately  pai'allel  to  the  shore.  The  rocks  on  the 
western  side  dip  east,  those  on  the  eastern  side  dip  more  steeply  west,  and 
the  general  structure  of  the  island  is  believed  to  be  a  syncline.  The  wash 
of  the  waves  has  cut  a  bench  into  the  east-dipping  shales  south  of  the  wharf 
on  the  western  side  of  Conanicut  (PI.  XXIII,  p.  352).  That  the  rocks  on 
this  island  have  been  less  metamorphosed  than  those  in  Hope  Island  has 
alread}^  been  noticed. 
moN  XXXIII 16 


CHAPTER    III. 

THE  WESTERN  SHORE  OF  THE  BAY. 

FROM  SAUNDERSTOWZST  TO   ZSTARRAGANSETT  PIER. 

ALONG   THE   SHORE. 

About  a  quarter  of  a  mile  south  of  Saunderstown  occurs,  along  the 
shore,  black  shaly  rock,  originally  a  very  fine-grained  carbonaceous  sand- 
stone, and  a  light-colored  coarser  quartzitic  rock,  representing  an  original 
coarse-grained  sandstone,  with  but  little  carbonaceous  material.  The  shaly 
rock  is  full  of  a  micaceous  mineral,  and  also  contains  black  specks,  which 
in  part  are  probably  biotite  and  in  part  some  other  mineral.  The  coarse- 
grained sandstone  has  black  mica  abundantly  disseminated  throughout  it, 
and  not  collected  in  patches  as  on  Hope  Island.  The  strike  is  N.  20°  E., 
dip  40°  E.  Southward  some  of  the  coarse-grained  sandstone  contains  white 
mica;  yet  farther  south  very  small  pebbles  begin  to  appear  in  the  sand- 
stone, usually  in  thin  layers,  forming  a  small  part  of  the  total  thickness  of 
the  sandstones.  Black,  shaly,  very  fine-grained  rock  continiTCS  to  be  inter- 
stratified  with  the  sandstones.  Strike  N.  30°  E.,  dip  often  as  low  as  25°  E. 
The  pebbles  are  usually  less  than  1  inch  long,  and  have  been  drawn  out 
and  flattened  by  shearing.  At  first,  black  shaly  rock  and  sandstone  alter- 
nate rather  frequently  just  north  of  a  small  stream  entering  the  bay;  sand- 
stone very  largely  predominates.  South  of  the  brook  there  is  again  an 
alternation  of  sandstones  and  black  shales,  and  the  low  dip  of  30°  E. 
becomes  40°  E.,  then  steeper,  until  it  is  soon  practically  vertical;  after 
which  the  dip  becomes  westward,  about  70°  W.  at  first,  and  finally,  at  a 
point  1,250  feet  north  of  the  South  Ferry  wharf,  it  is  40°  W.  Here  the 
section  is  cut  off'  transversely  to  the  strike  by  a  large  pegmatite  dike. 
South  of  this  dike  the  lowest  rocks  are  black  shales,  almost  horizontal,  over- 
lain by  quartziferous  sandstone  with  white  mica,  containing  small  pebbles, 
overlain  by  black  shale  dipping  20°  E.     The  low  eastward  dip  continues. 


THE  BONNET.  243 

almost  as  far  as  a  very  large  pegmatite  dike  about  600  feet  north  of  the 
South  Ferry  wharf,  just  north  of  which  the  dip  becomes  low  west.  South 
of  this  pegmatite  dike  the  low  eastward  dip  continues. 

North  of  South  Ferry  wharf  occurs  a  considerable  thickness  of  sand- 
stone of  rather  small  grain  and  somewhat  bluish  color,  with  black  shale 
higher  in  the  bank.  South  of  the  wharf  lig-hter-colored  sandstone  appears, 
with  very  small  pebbles  and  darker,  more  shaly  rock,  strike  N.-S.,  dip 
70°  E.  Farther  on  there  is  no  exposure  for  a  little  over  half  a  mile,  until 
the  northern  end  of  the  Bonnet  is  reached. 

At  the  north  end  of  the  Bonnet  there  is  sandstone  with  strike  N.  8°  E., 
dip  low  east.  A  very  large  pegmatite  dike  occurs  at  the  northeast  angle  of 
the  Bonnet.  South  of  this  dike  the  strike  is  N.  8°  E.,  dip  60°  E.  From 
here  to  the  southern  end  of  the  Bonnet  there  is  an  alternation  of  sandstones 
and  black  carbonaceous  shaly  rocks.  The  thickest  bed  of  the  black  shale 
has  a  thickness  of  at  least  40  feet.  The  strike  at  the  south  end  remains  the 
same,  N.  8°  E.,dip  steep  east,  near  the  water's  edge  as  low  as  45°;  steeper 
higher  on  the  banks,  as  high  as  60°  or  70°.  Whether  this  indicates  a  local 
flexure  or  a  syncline  toward  the  east  can  not  be  determined.  Some  of  the 
sandstones  are  very  quartzitic,  with  much  white  mica.  West  of  Bonnet 
Point  is  a  rapid  alternation  of  sandstones  and  black  shales  as  far  as  the 
beach.  The  frequency  of  coarse  quartz  grains  in  some  of  the  sandstones 
is  noticeable.     Strike  N.  8°  E.,  dip  60°  E. 

At  the  west  end  of  the  beach  south  of  Wesquage  Pond,  the  Carbonif- 
erous series  is  exposed  again.  The  beds  are  here  micaceous  sandstones 
with  darker  layers.  The  strike  is  parallel  to  the  shore,  N.-S.,  dip  15°  E. 
The  Carboniferous  series  terminates  about  200  feet  south  of  the  first 
exposure,  in  contact  with  a  very  thick,  coarsely  pegmatitic  dike.  This  dike 
borders  the  shore  southward  for  a  long  distance  (Pis.  XVIII,  XIX,  XXV), 
but  about  1,200  feet  north  of  Watsons  Pier  it  includes  small  fragments  of 
the  Carboniferous  sandstone,  and  almost  surrounds  a  very  large  mass  of  the 
Carboniferous.  The  dip  of  this  great  block  is  still  east.  The  large  area 
toward  the  east  of  the  large  pegmatite  dike  which  follows  the  shore  is 
believed  to  be  all  imderlain  by  Carboniferous  rocks  now  worn  away  by  the 
sea  and  covered  by  its  waters. 

Where  the  south  trend  of  the  shore  changes  to  the  southeastward,  toward 
Watsons  Pier,  the  sti-ike  brings  these  hidden  Carboniferous  rocks  again  into 


244  GEOLUGY  OP  THE  ]S"AREAGANSETT  BASIN. 

view,  with  a  strike  fault  contact  over  the  pegmatite;  strike  N.  3°  E.,  dip 
45°  E.  These  Carboniferous  rocks  are  chiefly  sandstone,  very  quartzitic, 
with  white  mica,  and  small  specks  formed  by  a  black  mineral.  Some  more 
carbonaceous,  darker  courses  come  in  just  north  of  the  boathouse.  Alterna- 
tions of  the  sandstone  and  darker  shaly  rock  continue  as  far  .as  120  feet 
beyond  Watsons  Pier;  strike  N.  7°  W.,  dip  60°  E.  Lighter  and  darker 
colored  sandstones  continue  to  form  the  shore  imtil  it  begins  to  turn  south- 
westward,  but  an  unusually  large  mass  of  pegmatite  borders  it  on  the  east. 
West  of  the  angle  just  mentioned,  which  is  a  southward-projecting  point  of 
pegmatite,  the  Carboniferous  sandstones  are  seen  again,  with  the  same 
strike,  but  with  a  nearly  vertical  dip.  Along  the  shore  southwestward 
the  Carboniferous  rocks  are  exposed  almost  as  far  as  the  mouth  of  a  small 
brook,  although  frequently  intersected  along  the  bedding  by  pegmatite 
veins,  often  of  considerable  size.  The  more  western  courses  are  decidedly 
black  carbonaceous  shales.  Before  reaching  the  mouth  of  the  little  stream 
pegmatite  occurs  in  great  abundance. 

About  three  fourths  of  a  mile  south  of  Watsons  Pier  the  coast  makes 
a  projection  a  little  like  the  Bonnet,  but  smaller.  This  projection  is  formed 
by  a  rock  looking  in  general  like  an  ordinary  light-colored  granite,  though 
showing  pegmatitic  veining  and  peg'matitic  structui-e  in  blotches.  West  of 
the  south  end  of  this  projection,  and  directly  west  of  Whale  Rock,  there 
appears  dark  shaly  rock,  with  some  sandstone  The  sandstone  is  in  places 
made  up  of  very  coarse  quartz  grains.  Some  of  the  shaly  rock  is  very 
carbonaceous;  strike  N.  25°  E.,  dip  about  vertical.  Along  the  more 
southerly  trend  of  the  shore  the  Carboniferous  rock  is  at  first  not  exposed, 
although  the  occurrence  of  the  pegmatite  offshore  only  in  the  form  of 
narrow  dikes  indicates  the  presence  of  the  intersected  clastic  rocks,  but 
farther  south  there  is  seen  a  conglomerate  with  pebbles  from  one-fourth  to 
one-half  an  inch  in  diameter,  quartzitic  as  a  rule.  The  angle  northeast  of 
the  Clump  Rocks  is  formed  by  pegmatite. 

The  western  of  the  Clump  Rocks  at  the  light-house  is  formed  by  an 
ordinary  granite  rock  of  medium  grain  with  pegmatitic  dikes  and  blotches. 
It  includes  near  the  top  a  mass  of  Carboniferous  quartzitic  sandstone,  with 
very  many  biotite  flakes.  The  included  piece  still  has  an  eastward  dip.  At 
the  water's  edge  on  the  west  side  is  a  long  mass  of  Carboniferous  rock  of 


NAREAl^ANSETT  PIEK.  245 

considerable  length,  of  darker  and  finer  grain,  showing  the  carbonaceous 
character  of  the  inclusion.     Strike  of  the  same,  N.  16°  E.,  dip  45°  E. 

A  third  of  a  mile  northwest  of  the  Clump  Rocks  the  pegmatite  incloses 
a  small  fragment  of  Carboniferous  shaly  sandstone. 

The  eastern  and  much  larger  hill  of  Boston  Neck  shows  frequent 
pegmatite  exposures  on  the  eastern  side  toward  the  top,  directly  west  of  Bon- 
net Point,  and  over  a  considerable  area  near  its  southern  termination,  south 
of  Watsons  Pier.  It  is  more  probable,  however,  that  this  hill  is  composed 
of  pegmatite  and  Carboniferous  rocks  in  frequent  alternation  than  that  it  is 
underlain  by  pegmatite  alone.  The  more  western  hill  contains  numerous 
exposures  of  granitic  rock  verging  into  pegmatite,  near  the  Narrows,  and 
a  few  exposures  of  the  same  rocks  on  the  western  side. 

On  Little  Neck  there  are  frequent  exposures.  They  were  not  carefully 
searched,  but  all  the  rocks  examined  were  granitic,  usually  medium  grained, 
whitish  or  reddish,  cut  by  pegmatite  dikes  or  containing  blotclies  of  peg- 
matite, the  pegmatite  being  unusually  coarse  just  west  of  the  north  end  of 
Beach  Pond,  where  the  micfi  plates  are  at  times  6  inches  broad. 

Between  the  two  old  wharves  at  Narragansett  Pier,  east  of  the  Casino, 
the  Carboniferous  rock  is  seen  again,  included  as  a  very  large  block  in  the 
granitic  rock.  It  is  chiefly  sandstone,  decidedly  quartzitic,  with  white  and 
black  mica,  the  latter  more  common  along  certain  layers  parallel  to  the 
stratification.  There  is  considerable  crumpling  in  this  rock,  especially 
toward  the  south  end.  The  rock  contains  also  a  layer  of  conglomerate. 
The  pebbles  are  so  much  drawn  out  and  flattened  along  the  plane  of  schis- 
tosity  that  they  appear  as  indistinctly  bordered  whiter  blotches  on  the  general 
rock  surfaces;  but  transverse  to  the  schistosity,  especially  along  their  shorter 
diameter,  their  outline  is  often  fairly  distinct.  They  are  usually  one-fourth 
of  an  inch  thick,  rarely  more  than  a  third  of  an  inch,  with  a  width  of  1  to 
1^  inches  and  a  length  of  3  to  4  inches.  No  one  who  had  followed  the 
Carboniferous  series  in  the  order  here  indicated  would  fail  to  recognize  the 
Narragansett  Pier  exposure  as  belonging  to  this  series. 

The  granite  at  the  pier  is  reddish  and  often  pegmatitic.  The  exposures 
were  followed  southward  for  2  miles  along  the  shore.  It  is  undoubtedly 
the  same  granite  as  that  on  Little  Neck  and  Boston  Neck.  Since  it  includes 
fragments  of  the  Carboniferous  series,  as  well  as  intersects  the  strata  of  this 
series,  it  must  be  of  more  recent  age.     This  subject  is  further  discussed 


246  GEOLOGY  OP  THE  NARRAGANSETT  BASIN. 

in  the  chapter  on  the  arkoses  and  conglomerates  of  the  Narragausett  Bay 
region  (Chapter  X). 

WEST  OF  THE  COVE  AND   PATTAQUAMSCOTT  RIVER. 

Pattaquamscott  River  and  the  cove  toward  the  southwest  were  once 
probably  occupied  by  the  Carboniferous  series,  now  removed  by  erosion, 
excepting  along  the  western  side  of  the  valley  formed  by  the  eastern  side 
of  Tower  Hill.  At  the  southern  end  of  this  hill,  north  of  the  railroad, 
the  rock  is  very  quartziferous  and  schistose.  The  schistosity  strikes 
N.  80°  E.  and  dips  60°  N.  In  certain  layers  the  rock  is  full  of  pebbles, 
chiefly  quartzitic,  but  with  also  some  granitic  ones.  The  pebbles  are  very 
much  elongated  and  flattened,  as  at  the  pier  exposure.  Farther  northeast 
the  conglomerate  pebbles  are  still  more  drawn  out.  The  pebbles  usually 
are  white,  bordered  by  a  greater  accumulation  of  black  mica  than  is  found 
in  the  general  mass.  As  the  lengthening  of  the  pebbles  continues,  a  point 
comes  where  there  appears  an  alternation  of  whiter  and  darker  thin  bands, 
in  which  only  a  person  familiar  with  such  studies  would  still  recognize 
the  pebble.  This  limit  has  here  been  reached.  Farther  down  the  hillside 
some  of  the  larger  quartzitic  and  granitic  pebbles  are  less  drawn  out,  and 
can  easily  be  recognized.  Some  of  the  larger  ones  are  1^  to  2  inches  long. 
Below  the  hotel,  farther  northeast,  the  rock  is  well  exposed.  From  the 
southern  end  of  Tower  Hill,  as  far  as  the  hotel,  the  Carboniferous  rocks  are 
frequently  cut  along  the  schistosity  by  dikes  of  ordinary  granite,  and  also 
by  the  pegmatite  phase  of  the  same,  into  which  it  merges  in  some  places, 
while  at  others  the  contrast  is  sharp.  The  result  is  a  rapid  alternation  of 
clastic  Carboniferous  rock  with  these  granitic  and  pegmatitic  dikes,  espe- 
cially well  shown  below  the  hotel.  The  alternation  of  Carboniferous  rocks 
and  the  pegmatitic  granite  occurs  for  a  distance  of  2  miles  along  the  east 
side  of  Tower  Hill.  The  schistosity  dips  westward.  Going  northward  no 
more  Carboniferous  rocks  are  encountered  until  the  old  plumbago  mine,  a 
little  over  half  a  mile  south  of  Bridgetown,  is  reached.  Above  the  mine  is 
a  good  exposure  of  a  dark,  very  micaceous,  and  probably  graphitic  schist. 
The  strike  of  the  schistosity  here  is  N.  5°  E.  and  the  dip  70^  E.  Farther 
down  the  hillside  a  great  quartz  vein  includes  scattered  and  brecciated  rem- 
nants of  the  Carboniferous  series;  among  others,  fragments  of  genuine 
black  plumbago,  unctuous  to  the  touch.     The  main  body  of  Tower  Hill, 


WEST  OF  THE  (JOVE  AND  PATTAQUAMSOOTT  EIVBR.  247 

and  its  northward  extension,  McSparran  and  Hammond  liills,  is  made  up 
of  the  granite,  reddish,  medium  to  finer  grained,  diked  and  blotched  by 
pegmatite.  Occasionally  there  is  a  slight  tendency  toward  schistosity  in 
some  of  the  outcrops. 

The  valley  of  Indian  Run  was  at  one  time  probably  also  occupied  by 
Carboniferous  rocks.  Near  the  southern  end,  toward  Peacedale,  several 
exposures  of  the  Carboniferous  still  I'emain.  Directly  east  of  Peacedale, 
on  the  southern  side  of  a  steep  hill,  partly  wooded,  a  strongly  metamor- 
phosed rock,  possibly  belonging  to  the  Carboniferous  series,  is  exposed; 
strike  N.  50°  E.,  dip  70°  SE.  The  rock  here  has  a  decidedly  gneissoid 
structure,  being  composed  of  white  quartz  with  white  and  black  micas  and 
some  other  black  mineral.  The  darker  minerals  are  often  arranged  in  layers 
between  the  lighter-colored  ones.  Some  of  the  whiter  streaks  may  repre- 
sent original  pebbles.  Apparently  some  of  the  larg-er  granitic  and  quartz- 
vein  pebbles  have  suffered  less  drawing  out  and  remain  more  recognizable. 
These  exposures  are  at  the  extreme  limit  of  macroscopically  recognizable 
clastic  rocks.  Farther  up  the  hillside  occurs  a  reddish  porphyritic  gneiss, 
apparently  representing  a  granite  with  phenocrysts  of  feldspar.  All  rocks 
named  are  cut  by  the  regular  reddish  granite  with  pegmatite  blotches  and 
dikes.  Similar  exposures  of  the  gneissoid — possibly  Carboniferous — rock 
occur  where  the  road  east  from  Peacedale  crosses  Indian  Run. 

On  Rose  Hill,  west  of  Mooresfield,  occurs  the  granite  with  pegmatitic 
variations.  Apparently  the  more  gneissoid  form,  with  crushed  and  stretched 
porphyritic  feldspars,  also  occurs  here.  Directly  north wai'd  2^  miles,  on 
Congdon  Hill,  more  granite  occurs.  Some  of  it  is  the  ordinary  type  of 
these  regions,  with  pegmatitic  phases.  Other  portions  appear  gneissoid,  and 
some  exposures  here  are  similar  to  the  gneissoid  Carboniferous  schists  east 
of  Peacedale. 

It  is  evident  that  the  extreme  western  limit  of  rocks  whose  clastic 
origin  can  readily  be  recognized  has  here  been  reached.  This  is  not  equiv- 
alent, however,  to  asserting  that  the  original  western  limit  of  the  Carbonif- 
erous deposits  of  the  Narragansett  Basin  in  this  direction  has  been  attained. 
It  is  probable  that  they  once  extended  farther  westward,  but  in  the  limited 
time  at  the  writer's  command  detailed  study  of  these  more  western  areas 
was  not  possible. 


248  GEOLOGY  OF  THE  NARRAGANSETT  BASIN. 

froji  saunderstown  to  wickford. 

North  of  Saunderstown  the  same  series  occurs  that  is  exposed  along  the 
shore  from  Samiderstown  to  Nari'agansett  Pier.  Except  for  a  short  distance 
between  Caseys  and  Greenes  points  the  exposm'es  are  all  confined  to  the 
more  inland  districts.  Most  of  the  outcrops  are  sandstones.  The  softer, 
more  finely  grained,  and  more  carbonaceous  sandstones,  almost  possessing 
the  character  of  shales,  are  more  rarely  seen  than  south  of  Saunderstown. 
This  may  mean  that  unequal  erosion  has  left  their  former  line  of  outcrop 
beneath  the  present  level  of  the  soil,  or  that  they  were  rarer  in  the  area 
northwest  of  Saunderstown.  The  facts  noted  in  the  field  point  rather  to  a 
diminution  in  the  frequency  of  the  darker,  shaly  strata.  The  rocks  corre- 
sponding best  to  the  shale  seem  to  be  less  carbonaceous  than  southward, 
and  merge  into  fine-grained  sandstones  only  sufficiently  carbonaceous  to 
give  them'  a  very  dark,  but  rarely  a  really  black,  color. 

Where  first  exposed  north  of  Caseys  Point,  the  dip  of  the  sandstone 
is  about  vertical.  At  the  beginning  of  the  continuous  exposures  the  strike 
is  N.  6°  E.,  dip  35°  E.  The  coarser  sandstone  is  very  quartzitic,  white, 
with  abundant  white  mica,  spotted  with  a  more  scattered  black  micaceous 
mineral.  The  cross  stratification  is  often  marked  (PI.  XX).  This  sandstone 
contains  frequent  thin  conglomeratic  layers,  with  pebbles  up  to  1.^  or  2 
inches  in  diameter.  The  pebbles  are  usually  quartzitic,  occasionally  gran- 
itic. Interbedded  with  these  rocks  are  darker,  more  carbonaceous,  finer- 
grained  courses.  Going  northward  toward  the  quarry  a  rather  thick  layer, 
more  carbonaceous  than  usual  in  this  more  northern  area,  borders  the 
shore.  Here  the  strike  is  N.  10°  W.,  dip  45°  E.  A  pegmatite  dike  cuts 
the  rock  parallel  to  the  strike.  A  darker,  finer-grained,  more  ferruginous 
dike  also  seems  to  occur.  The  alternation  of  finer-grained,  more  carbon- 
aceous rock,  coarser  white  sandstones,  and  occasional  thin  pebble  layers 
continues  as  far  as  Hazzard's  quany.  Here  the  strike  is  N.°  8  E.,  dip 
perhaps  60°  E. 

From  this  quarry  westward,  as  far  as  the  angle  in  the  road  connecting 
Saunderstown  and  Hamilton,  there  are  a  number  of  good  exposures  on  the 
hillside.  The  large  exposure  at  the  quarry  consists  almost  entirely  of  white 
sandstone.  At  the  house  on  the  hillside  tliere  occur  wide  layers  of  a  dark- 
blue,  very  fine-grained  shaly  rock,  which  takes  the  place  of  the  much  more 


,   GEOLOGICAL  SURVE' 


CROSS-STRATIFICATION    IN    PEB  BLY  SAN  DSTON  E   OF    KINGSTOWN    SERIES,   DEVILS    FOOT    LEDGE,   KINGSTOWN,   RHODE    ISLAND. 


FEOM  SAUNDEESTOWN  TO  WICKFOED.  249 

carbonaceous  shales  south  of  Saunderstown ;  dip,  50°  E.  Farther  west  the 
sandstone  contams  conglomeratic  streaks;  dip,  65°  E.  Still  farther  west  is 
sandstone  with  a  few  scattered  pebbles,  rarely  2  inches  long.  The  coarser 
sandstones  contain  fragments  looking  like  altered  clastic  feldspar  grains, 
obtained  from  some  more  ancient  granitic  area.  Coarser  and  darker  fine- 
grained sandstones  occur  westward  as  far  as  the  road  angle  mentioned 
above.  The  next  exposure  of  the  section  lies  on  the  western  slope  of 
Barbers  Height,  on  the  north  side  of  the  road  toward  Hammond  Hill  and 
three-fourths  of  a  mile  from  the  shore;  strike  N.  10°  W.,  dip  80°  E.;  coarse 
white  sandstone  and  darker  finer-grained  rock  with  black  mica.  On  the 
south  side  of  the  road,  hardly  a  quarter  of  a  mile  farther  westward, 
both  kinds  of  sandstone  occur.  The  coarser  contains  granite  pebbles.  A 
pegmatite  dike  is  here  poorly  exposed. 

Northward  along  the  trend  of  the  hill  called  Barbers  Height  the 
coarse  white  sandstones  and  dark  finer-grained  rocks  continue  to  be 
exposed.  The  darker,  more  carbonaceous,  fine-grained  shaly  rock  has  a 
slightly  purplish  tinge  at  several  points  along  the  roadside.  The  most 
marked  change  toward  the  northern  end  of  the  height  is  a  more  north- 
westerly strike,  corresponding  to  the  change  in  the  trend  of  the  granite 
hill  on  the  southwest,  and  a  much  lower  eastward  dip,  usually  not  exceeding 
40°  E. 

At  the  angle  of  the  road,  1^  miles  south  of  Hamilton,  on  the  way  to 
Hammond  Hill,  there  are  numerous  exposures.  The  dips  are  usually  about 
30°  E.  The  strikes  are  northerly,  but  variable.  No  sharply  defined  bed- 
ding planes  assist  in  determining  the  plane  of  stratification.  A  pegmatite 
dike  occurs  behind  a  barn  near  the  southeastern  end  of  the  set  of  exposures. 
It  is  one  of  the  most  northerly  of  these  pegmatite  dikes  in  the  Carboniferous 
area.  About  a  quarter  of  a  mile  east  of  this  locality  the  strike  is  N.  10°  W., 
dip  40°  E.,  well  shown.  Northward  less  than  a  quarter  of  a  mile,  at  the 
angle  of  the  road,  the  strike  is  distinctly  west  of  north,  how  much  is 
unknown,  perhaps  N.  20°  W.,  dip  30°  E.  Northeastward  in  the  field  the 
strike  is  N.-S.,  dip  30°  E.,  well  shown.  The  last  exposure,  lying  north 
of  a  stone  wall,  shows  a  change  of  strike  to  N.  25°  W.,  dip  20°  E.,  well 
shown  by  dark  carbonaceous,  fine-grained,  shaly  rock  overlying  the 
coarser  whiter    sandstone.     Another  of    these   marked   changes   of   strike 


250  GEOLOGY  OF  THE  NARRAGANSETT  BASIN. 

toward  the  northwest  is  seen  northeast  of  the  hist  exposure,  near  the  north- 
east end  of  the  most  northerly  walled  field  on  the  hill.  Here  a  strike  of 
N.  12°  W.  becomes  N.  40°  W.  in  a  very  short  distance  northward.  The 
dip  is  steeper  than  usual  here,  60°  E.  The  most  northern  exposures, 
near  the  cove,  show  a  northwesterly  strike  and  an  eastward  dip  of  about 
35°,  as  nearly  as  it  can  be  determined. 

The  next  set  of  exposures  westward  is  at  the  angle  of  the  road  a  little 
over  a  quarter  of  a  mile  south  of  Hamilton.     Here  the  strike  is  N.  30°  W., 
dip  65°  E.,  rather  well  shown  by  the  contrast  of  the  dark  finer-grained  and 
the  coarser  white  sandstone.     The  latter,   in  places,   contains  very  small 
pebbles.     West  of  Hamilton   a  quarter  of  a  mile   a  road  leads  northwest- 
ward and  connects  with  another  road  leading  to  Wickford.     Along  both 
sides  of  the  first  road  exposures  are  numerous.     One  near  the  road  gives  a 
strike  of  N.  40°  W.,  dip  about  45°  E.;  there  is  contoi'tion  along  the  strike. 
Along  the  ridge  at  the  western  end  of  a  row  of  houses,  south  of  a  pond, 
the  strike  is  N.  12°  W.,  changing  to  N.  20°  W.,  dip  apparently  50°  to  60° 
E.     North  of  this  pond  considerable  coaly  fine-grained  rock  is  shown  on 
the  south  side  of  the  road,  with  apparently  a  nearly  horizontal  bedding  and 
a  slight  dip  northeastward.     On  the  eastern  side  of  the  connecting  road 
to  Wickford  there  are  good  exposures  upon  a  rather  high  hill.     Toward 
the  north,  one  exposure  exhibits  a  strike  of  N.  18°  W.,  dip  60°  E.,  finely 
shown  by  a  very  carbonaceous,  fine-grained  shaly  layer  in  the  coarser  white 
sandstone.     In  this  entire  series  of  rocks  the  coarser  white  sandstones  pre- 
vail; they  contain  but  few  pebbles  and  these  are  always  small.     Finer- 
grained,  more  carbonaceous  layers,  with  ottrelite  locally,  occur  here  more 
frequently  than  to  the  westward.     Wesf  of  Hamilton,  toward  Indian  Corner 
(marked  Allenton  on  the  maps),  about  halfway  between  the  two  villages,  a 
large  exposure  on  the  south  side  of  the  road  shows  a  strike  of  N.  20°  W,, 
dip  45°  E.,  well  exhibited  by  alternating  dark  fine-grained  rock  and  white 
coarse  sandstone.     Around  Indian  Corner,  exposures,  chiefly  of  coarse  sand- 
stone, often  with  pebbles,  are  numerous.     The  strikes  are  variable,  being  on 
the  average  N.  27°  W.,  dip  30°  to  45°  E.     A  little  over  half  a  mile  south 
of  Indian  Corner,  in  the  roadside  and  northeast  of  the  house,  a  bluish  Car- 
boniferous sandstone  shows  strike  N.  45°  W.,  dip  50°  E.     This  occurrence 
agrees  very  well  with  the  apparent  northwesterly  trend  of  the  line  of  granite 


FEOM  WICKFORD  TO  EAST  GREENWICH.  251 

bordering  the  Carboniferous  field   in  this  direction   from  Hammond   Hill 
beyond  Congdon  Hill. 

As  already  stated,  the  exposures  from  Saunderstown  to  Wiekford  and 
westward  are  a  northward  extension  of  the  series  which  is  developed  to 
the  southward  as  far  as  Narragansett  Pier. 

FROM  WICKFORD  TO  FAST  GREENWICH. 

Northward  of  Wiekford,  as  far  as  East  Greenwich,  the  rocks  last  above 
described  continue  to  occur,  but  there  is  a  marked  change  in  their  dip,  the 
general  dip  being  westerly,  except  on  Potowomut  Neck,  where  the  strike 
swings  around  to  the  northeast,  and  more  or  less  irregular  folding  gives 
both  northwesterly  and  southeasterly  dips. 

The  most  western  exposures  occur  about  a  mile  south  of  Davisville, 
along  the  railroad.  Here  a  bluish  sandstone,  with  conglomeratic  layers 
and  carbonaceous  color  banding,  shows  strike  N.-S.,  dip  45°  W.  East  of 
these  exposures,  about  half  a  mile  west  of  the  road  between  Wiekford  and 
East  Greenwich,  on  the  north  side  of  the  connecting  road  toward  Davis- 
ville, abundant  exposures  show  strike  N.  12°  W.,  dip  70°  W.  Along  the 
western  side  of  the  main  road  itself  exposures  are  frequent  for  a  distance 
of  about  2  miles  north  of  Wiekford.  One  of  the  more  southern  exposures, 
on  a  hill  west  of  the  road,  shows  strike  N.  40°  E.,  dip  very  steep,  about 
vertical,  perhaps  slightly  east.  A  quarry  near  the  northern  end  of  this 
series  shows  a  strike  of  N.  18°  E.,  dip  85°  W.,  well  marked  by  narrow 
carbonaceous  color  banding  in  a  coarse  sandstone.  North  of  this  quarry  a 
short  distance  a  road  goes  eastward;  1^  miles  eastward  along  this  road  a 
road  goes  northward.  Along  this  road  occurs  an  exposure  of  a  very  car- 
bonaceous, possibly  ottrelitic,  sandstone  with  strike  N.  20°  E.  and  dip 
westerly.  About  1^  miles  directly  north  of  this  exposure,  on  the  south- 
east side  of  a  road,  there  is  sandstone  with  thin  pebble  layers.  There 
seems  to  be  a  very  low  northerly  dip  of  the  rocks  here,  nearly  horizontal. 
The  most  easterly  exposures  occur  west  of  Clarks  Point,  along  the  west 
side  of  the  road,  as  far  north  as  Halls  Creek.  The  strike  on  the  average 
is  N.-S.,  the  dip  20°  W.  About  IJ  miles  northwest  of  Aliens  Harbor 
and  1  mile  south  of  Potowomut  River  there  is  a  large  exposure  north  of  a 
schoolhouse  at  the  road  corner.     The  rock  here  is  largely  of  the  fine-grained, 


252  GEOLOGY  OF  THE  NAERAGAJSTSETT  BASIN. 

black,  carbonaceous  type,  especially  along  the  northwestern  side  of  the 
exposure,  interstratified  with  which  is  coarser  white  sandstone.  Both  rocks 
contain  garnets,  and  the  shaly  rock  is  ottrelitic.  Strike  N.  23°  E.,  dip 
about  45°  W. 

Toward  the  western  end  of  Potowomut  Neck,  near  a  residence  north 
of  the  road,  are  numerous  exposures  of  sandstone  with  strike  N.  50°  E., 
dip  35°  N.,  on  the  western  end  of  the  exposures.  Toward  the  eastern  end 
of  the  neck  a  series  of  exposures  extend  from  the  Potowomut  Rocks  directly 
southward  nearly  to  the  Potowomut  River.  The  general  trend  of  the  rocks 
is  northeasterly,  but  it  is  evident  that  considerable  irregular  flexuring  or 
folding  has  taken  place,  so  that  the  strikes  are  very  irregular,  and  the  dips  are 
both  northerly  and  southerly,  according  to  the  particular  locality  observed. 
While  therefore  unsatisfactory  for  purposes  of  stratigraphy,  these  exposures 
are  still  worthy  of  close  examination,  because  they  show  some  very  inter- 
esting phenomena  connected  with  the  shearing  of  these  rocks  more  or  less 
perpendicular  to  the  bedding  and  the  consequent  interpenetration  of  the 
frayed  surfaces  of  the  adjoining  layers.  The  more  carbonaceous  layers  in 
the  exposures  west  of  the  house  -north  of  the  road  show  garnets  and  other 
minerals,  the  products  of  metamorphism ;  one  of  these  minerals  occurring 
in  the  rock  is  columnar,  black,  with  frayed  expanded  ends.  While  a  large 
part  of  the  rock  exposures  are  coarse  white  sandstone  or  finer-grained  black 
shaly  rocks,  as  in  the  rest  of  the  series  described  in  this  area  and  south- 
ward, yet  there  is  a  very  large  exposure,  west  of  the  buildings  north  of  the 
road,  of  a  greenish  shaly  rock,  spotted  with  the  stained  marks  caused  by 
the  weathering  of  some  pyritiferous  mineral,  which  is  very  unusual  in  the 
series.  The  strike  at  the  Potowomut  Rocks  seems  to  be  N.  50°  E.,  dip 
apparently  steep  northwest. 

WESTERN    BORDER    OF     THE    CARBOISTIFBROITS    BASIIST,    FROM    EAST 
GREEIS^VICH  TO  NATICK  A:N^D  NORTHWARD  INTO  CRANSTON. 

The  present  western  border  of  the  Carboniferous  basin  of  the  Narra- 
gansett  region  extends  from  East  Greenwich  southwesterly,  west  of  Davis- 
ville  and  Wickford  Junction.  At  East  Greenwich  the  pre-Carboniferous 
rocks  form  the  steep  hillside  above  the  town.  At  a  road  corner  near  the 
top  of  the  hill,  in  a  line  almost  directly  west  of  the  Potowonuit  Rocks, 
these  more  ancient  rocks  are  well  exposed  in  a  quarry.     The  rock  here  is 


EAST  GKEENWIOH  TO  NATICK.  253 

very  fine  grained  and  white,  with  minute  black  specks.  The  cleavage 
planes  lie  E.-W.,  dip  low  northerly.  The  western  border  of  the  Car- 
boniferous basin  probably  follows  the  steep  hillside  from  East  Greenwich 
to  Coweset,  and  thence  for  some  distance  the  northern  side  of  Drum  Rock 
Hill.  The  presence  of  (1)  granite  exposures  near  the  southeastern  end  of 
the  hill,  half  a  mile  west  of  the  southern  end  of  Grortons  Pond;  (2)  a  fine 
exposure  of  the  quartzite  and  schist  series  at  the  northern  end  of  the  same 
hill,  hardly  a  sixth  of  a  mile  east  of  Natick;  (3)  an  exposure  of  the  same 
series  on  the  western  side  of  the  hill,  a  quarter  of  a  mile  south  of  the  last 
locality,  and  (4)  a  series  of  exposures  southwest  of  the  third  locality,  along 
the  road  leading  directly  south  from  Natick,  in  order — quartzite,  then  gran- 
ite, then  quartzite  again — tends  to  show  that  the  present  western  border 
passes  only  a  quarter  of  a  mile  west  of  Gortons  Pond  and  thence  north- 
westerly to  Natick.^ 

From  Natick  northward  the  basal  rocks  of  the  Carboniferous  series 
form  the  steep  hill  front  for  a  distance  of  at  least  2  J  miles,  while  the  eastern 
line  of  outcrops  of  the  pre-Carboniferous  series  can  be  traced  far  northward 
into  Cumberland. 

The  greatest  interest  in  this  border  line,  however,  centers  in  the  com- 
paratively small  stretch  of  2^  miles  from  Natick  northward,  since  here  the 
Carboniferous  beds  can  be  seen  resting  on  the  pre-Carboniferous  series,  the 
basal  beds  containing  very  many  angular  fragments  and  rounded  pebbles 
derived  from  the  older  rocks,  the  material  of  these  pebbles  varying  with 
the  character  of  the  underlying  rocks  immediately  adjoining.  All  grada- 
tions may  be  seen,  from  the  most  angular  fragments  to  well-rounded 
pebbles. 

The  quartzite-schist  series  is  well  exposed  along  the  north  side  of  Bald 
Hill  northward  as  far  as  Natick,  especially  west  of  the  town.  Near  the 
center  of  Natick  a  road  leads  up  the  very  steep  hill  west  of  the  town.  Just 
north  of  the  beginning  of  this  road  is  a  church,  below  which  the  quartzite 
series  is  exposed.  Ascending  the  road  for  a  distance  of  perhaps  100  feet, 
turning  northerly  into  a  group  of  houses,  the  observer  discovers  a  fine 
exposure  of  the  Carboniferous  base  resting  against  the  quartzite  on  the  west. 

'  The  evidence  leads  me  to  believe  that  the  margin  of  the  Carbonilerous  field  originally  lay  much 
farther  to  the  west.     It  is  likely,  indeed,  that  it  may  have  merged  with  what  is  now  the  Worcester 

li.isiu.— N.  S.  S. 


254  GEOLOGY  OF  THE  NAREAGANSETT  BASIN. 

The  bed  is  rather  bluish  and  dark  in  color,  and  contains  very  angular 
and  rather  separated  fragments  of  white  quartzite,  producing  a  striking 
effect  on  account  of  the  differences  of  color  and  the  consequent  distinctness 
of  outline  of  the  fragments.  This  effect  is  heightened  by  the  comparative 
rarity  of  the  bits.  From  this  cluster  of  houses  a  short  footpath  leads 
west  up  the  steep  hill  to  the  house  of  Mr.  Alexander  McTeer.  Northeast 
of  his  house  an  equally  striking  exposure  is  met,  the  rock  here  being  a 
great  mass  of  very  distinctly  outlined,  very  numerous  angular  fragments 
of  quartzite  embedded  in  a  slightly  darker  cement.  From  this  point  the 
basal  Carboniferous  conglomerate  forms  the  northeastern  face  of  the  hill, 
the  underlying  quartzites  being  often  well  exposed  just  southwest  of  the 
brow  of  the  hill.  It  often  requires  close  observation  to  distinguish  quartz- 
ites, where  brecciated  in  situ,  from  the  overlying  breccia- conglomerate 
series  which  forms  the  base  of  the  Carboniferous.  Southwest  of  the  road 
corner,  where  the  present  western  border  of  the  Carboniferous  area  makes 
a  sharp  curve  toward  the  east  of  north,  the  underlying  beds  are  of  a  pecu- 
liar greenish  rock,  often  seen  northward,  as  far  north  as  the  Cumberland 
district,  where  it  is  copper  bearing.  The  quartziferous  basal  layer  with 
angular  fragments  lies  west  of  the  road.  At  the  edge  of  the  roadbed 
southwest  of  the  road  corner  mentioned,  on  the  east  side,  the  overlying 
carbonaceous  black  shaly  rock  is  exposed,  dipping  under  a  coarse  sandstone. 
Strike  N„  30°  W.,  dip,  as  inight  be  expected,  50°  E.  The  presence  of  this 
carbonaceous  bed  so  near  the  border  of  the  Carboniferous  basin,  and  so 
near  the  base,  is  very  interesting,  especially  since  the  basal  bed  is  so 
conglomeratic. 

The  basal  quartzitic  conglomerate  beds  are  well  exposed  west  of  the 
road  north  of  the  road  comer  already  mentioned.  They  rest  here  on 
granite.  There  evidently  is  a  sharp  curve  in  the  border  line.  The  expo- 
sures can  be  followed  back  of  the  house  tln-ough  the  woods  for  a  sixth  of 
a  mile.  At  one  exposure  along  the  roadside  the  basal  bed  contains  granite 
pebbles  over  a  foot  in  diameter.  After  this  the  basal  series  must  be  fol- 
lowed along  the  east  side  of  the  road  through  the  woods.  Here  the  rocks 
are  a  coarse  quartzitic  sandstone.  Pebbles  are  not  numerous,  and  as  a 
rule  they  are  rather  small.  The  sandstone  can  be  readily  followed  through 
the  woods  to  a  fine  waterfall,  the  existence  of  which  would  not  be  suspected 
from  the  road.     Here  it  is  well  exposed;   strike  N.  40°  E.,  dip  60°  E.     Thin 


FROM  NATICK  NOllTHWARD.  255 

carbonaceous  bands  assist  in  showing  the  bedding.  The  series  can  be 
traced  into  the  open  field  northward.  Here  it  rested  formerly  upon  granite 
and  schistose  rocks.  An  exposure  in  the  open  district,  just  east  of  the  road, 
isolated  from  the  rest,  shows  among  the  pebbles  also  one  derived  from  the 
gneissoid  schist,  an  interesting  occurrence,  since,  in  spite  of  the  abundance 
of  the  schistose  rock  in  the  vicinity  of  the  basal  sandstone  and  conglom- 
erate series,  pebbles  from  the  schist  are  rarely  found.  The  schist  does  not 
seem  to  have  furnished  many  pebbles,  but  broke  up  into  a  fine  grit  on 
aerial  degradation  and  furnished  part  of  the  finer  material  of  the  overlying 
series.  The  granites  also  must  have  been  considerably  decayed.  The 
alteration  products  of  the  feldspars  drifted  farther  away  from  the  land, 
but  the  quartzitic  material  remained  nearer  the  shore  to  form  the  cement 
of  the  basal  conglomerates  and  the  overlying  arkose  and  sandstones;  but 
pebbles  of  granite  are  by  no  means  uncommon,  although  quartzite,  on 
account  of  its  greater  durability,  formed  the  predominating  pebbles  of  the 
basal  conglomerates. 

The  basal  series  of  arkoses  and  sandstones,  with  scattered  pebbles,  may 
be  traced  east  of  the  road  to  a  point  about  a  mile  north  of  the  road  corner, 
where  the  sharp  bend  in  the  western  border  of  the  Carboniferous  area  occurs. 
Here  the  basal  beds  rest  upon  a  varied  group  of  rocks — gneissoid  schists,  a 
peculiar  greenish  rock  of  the  type  found  in  Cumberland,  and  granite.  North 
of  this  point  the  basal  series  crosses  the  road  and  follows  it  along  its  west- 
ern side,  resting  upon  granite  as  far  as  the  next  road  corner  northward.  A 
house  stands  east  of  the  road  near  the  point  where  the  basal  series  crosses 
the  way.  A  short  distance  north  the  road  crosses  a  stream.  Up  the  stream 
westward,  in  the  woods,  the  basal  series,  only  moderately  conglomeratic 
with  granite  pebbles,  may  be  seen  well  exposed.  A  quarter  of  a  mile  from 
the  northern  road  corner  the  very  steep  hillside  is  formed  by  white  coarse 
sandstone,  with  layers  of  small  pebbles  and  occasional  scattered  angular 
pebbles,  some  of  them  as  much  as  9  inches  in  diameter;  some  of  the  latter 
are  granite.  The  underlying  rock  is  granite.  From  this  point  the  basal 
series  can  be  followed  to  a  short  distance  south  of  the  road  corner,  behind 
a  barn,  where,  in  an  open  field,  there  is  a  fine  exposure  of  the  series 
overlying  the  granite;  conglomerate  layers  are  frequent,  often  with  large 
pebbles,  some  of  these  of  granite,  the  greater  part  of  quartzite.  From  this 
point  the  basal  series  passes  northerly  to  a  point  west  of  the  road  corner,  a 


256  GEOLOGY  OF  THE  NAERAGANSETT  BASIN. 

third  of  a  mile  distant.  This  exposure,  along  the  western  road,  is  very 
interesting  on  account  of  the  extreme  lengthening  and  flattening  which 
many  of  the  pebbles  have  undergone  in  consequence  of  shearing.  The 
pebbles  consist  of  quartzite  and  granite.  Those  of  larger  size,  embedded 
in  the  softer  cement,  have  been  less  sheared  and  can  be  more  readily  recog- 
nized. The  basal  conglomerates  continue  to  be  shown  along  the  western 
side  of  the  road  to  Knightsville,  resting  toward  the  south  upon  granite, 
and  farther  north  upon  schists.  Where  the  basal  series  fails  to  be  exposed, 
the  western  border  of  the  Carboniferous  area  can  still  be  recognized  by  the 
steep  hillsides  formed  by  the  older  pre-Carboniferous  rocks.^ 

ROCKS    EAST    OF    THE    WESTERN    BORDER    OF    THE   CARBO^^^IFEROUS 
AREA  IN  WARWICK  AISTD  SOUTHERN  CRANSTON. 

The  basal  series  of  rocks  are  quartzitic  sandstones  of  white  color. 
Overlying  them  are  bluish  sandstones  and  coaly  shales.  The  coaly  shale 
east  of  the  great  bend  in  the  western  border  of  the  Carboniferous  area 
northwest  of  Natick  has  already  been  mentioned.  At  the  northern  end  of 
the  village,  along  a  connecting  road  west  of  the  river,  blue  sandstone  with 
darker  courses,  and  a  few  conglomerate  layers  with  small  pebbles,  are  well 
exposed.  Strike  N.-S.,  dip  45°  E.  A  sharp  change  in  the  strike  must 
take  place  in  Natick,  as  already  indicated  in  connection  with  the  description 
of  the  border  line. 

Along  the  road  from  western  Pontiac  northward  a  number  of  expo- 
sm-es  occur.  They  indicate  the  presence  of  bluish  sandstone,  with  small 
pebbles,  and  bluish-black  ottrelitic  shaly  rock  along  the  western  side  of  the 
hill  east  of  the  New  York,  New  Haven  and  Hartford  Railroad.  The  strike  is 
northerly  and  the  dip  10°  E.  The  entire  hill  and  the  valley  on  the  west 
is  probably  underlain  by  an  alternating  series  of  blue  sandstones,  often  with 
conglomeratic  layers  and  bluish-black  or  black  ottrelitic  shales.  Coaly  beds 
are  common  on  the  east  side  of  this  line  of  hills,  and  were  formerly  mined 
fai'ther  northward,  at  the  well-known  mines  northeast  of  the  Reform  School 
on  Sockanosset  Hill,  on  the  east  side  of  Rocky  Hill,  which  geologically 
is  a  continuation  of  Sockanosset  Hill,  and  still  farther  northward  in  the 
Valley  Falls  district.     This  series  of  coaly  rocks  not  far  above  the  base  of 

'  In  my  opinion  this  cliff  is  not  an  old  shore  escarpment,  bnt  is  due  to  the  deformation  of  the  old 
floor  of  the  basin  and  the  subsequent  erosion  of  the  soft  beds  which  lie  against  it. — N.  S.  S. 


WAEWIGK  AND  SOUTHERN  CRANSTON.  257 

the  Carboniferous,  extending  along  the  western  border  of  the  Carboniferous 
field,  often  presenting  workable  coals,  was  well  recognized  by  early  investi- 
gators of  this  district,  many  of  the  mines  dating  back  more  than  fifty  years, 
though  all  save  one,  that  at  Valley  Falls,  are  now  totally  abandoned. 

The  most  southern  exposure  on  the  east  side  of  Sockanosset  Hill  is 
half  a  mile  south  of  the  State  almshouse,  near  the  railroad.  The  medium- 
grained  sandstone  is  bluish;  the  coarser,  whitish.  Quartz  pebbles  up  to 
1^  inches  in  diameter  occur  in  the  conglomeratic  layers.  The  series  dips 
10°  NE.  In  front  of  the  almshouse  are  black  ottrelitic  shales.  Toward 
the  northeastern  side  of  the  building,  and  thence  for  a  rather  long  distance 
through  the  grounds,  more  sandy  bluish  sandstones,  occasionally  conglom- 
eratic, occur,  merging  into  fine-grained  rocks,  and  these  into  greenish  and 
bluish  shales,  in  part  ottrelitic.  The  strike  of  the  series  is  north-south,  car- 
rying the  rocks  east  of  the  Reform  School.  The  dip  is  20°  E.  The  finer- 
grained  rocks  and  shales  rather  predominate  in  this  series,  and  may  also  be 
seen  near  the  almshouse,  east  of  the  road.  In  the  vicinity  of  the  Reform 
School  and  of  the  reservoir,  exposures  of  bluish  sandstone  and  ottrelitic 
shales  occur.  The  coaly  beds,  including  the  workable  coals,  occur  half- 
way down  the  eastern  hillside  and  thence  down  into  the  valley  region. 
The  strike  of  the  rocks  is  north-south,  the  dip  low  east — usually  20°  E. — 
except  toward  the  mine,  where  the  dip,  according  to  the  miners,  increases 
to  about  50°  E.  If  this  is  true,  it  is  a  local  flexure,  the  dips  eastward  being 
low  again.  The  existence  of  such  a  flexui-e  seems,  however,  to  be  supported 
by  indications  northward,  the  dip  at  Wayland  Station,  on  the  northwest 
side  of  Sockanosset  Hill,  being  20°  to  30°  E.,  while  on  the  eastern  side  of 
Rocky  Hill  it  is  40°  to  70°  E. 

Eastward  of  the  Pawtuxet  River,  however,  the  exposures  show  low 
dips  again.  Along  the  railroad  north  of  Hills  Grove  Station,  black,  often 
coaly,  shales  lie  almost  horizontal.  North  of  the  road  corner  east  of  the 
station  a  quarry  shows  abundant  sandstone  with  a  northward  dip  of  about 
20°.  A  third  of  a  mile  north  of  the  station,  west  of  the  railroad,  abundant 
sandstone  with  conglomeratic  layers  shows  a  northeastward  dip  of  20°.  The 
sandstone  contains  steins  of  calamites,  longitudinally  coarsely  corrugated 
stems,  undeterminable  flattened  stems,  and  leaf-like  impressions,  1  or  2 
inches  wide  and  15  to  30  inches  long.     Similar  forms  may  be  recognized 

MON  XXXIII 17 


258  GEOLOGY  OF  THE  NARRAGANSETT  BASIN. 

ill  the  Silver  Spring  region.  A  quarter  of  a  mile  southwest  of  Norwood 
Station,  west  of  the  railroad  crossing,  numerous  exposures  of  sandstone 
having  a  low  easterly  dip  occur. 

WARWICK    ISTBCK. 

Eastward  of  Hills  Grrove  and  Norwood  stations  there  are  no  exposures 
in  Warwick  until  Warwick  Neck  is  reached.  In  the  railway  cut  west  of 
the  main  road  passing  along  the  length  of  the  neck,  black  carbonaceous 
shales  and  some  sandstone  courses  dip  in  a  northerly  direction.  West  of 
the  same  road,  a  quarter  of  a  mile  south  of  the  highest  point  of  the  neck, 
sandstone  is  exposed.  East  of  the  highest  point  of  the  neck  the  hill- 
sides, sloping  steeply  to  the  shore,  show  frequent  exposures  of  sandstone 
dipping  at  an  angle  of  about  40°  E.  Nearer  the  foot  of  the  hill  carbona- 
ceous dark  shales  make  their  appearance.  The  sandstone  continues  to  be 
well  exposed  for  about  a  fifth  of  a  mile  southward.  Northeast  of  these 
exposures,  north  of  a  small  pond  where  the  shore  turns  northeastward  to 
Rocky  Point,  black  shales  dip  low  eastward.  Corresponding  bluish-black 
shales  and  fine-grained  sandstones  are  found  a  quarter  of  a  mile  north- 
ward, along  the  road  to  Bay  Side.  There  occur  in  succession,  eastward: 
Sandstone,  forming  the  south  end  of  the  high  ridge  east  of  the  road  last 
mentioned;  conglomerate,  forming  the  middle  and  northern  part  of  this 
ridge;  sandstone,  exposed  at  the  northeast  of  the  northern  end  of  the  ridge 
and  on  the  western  side  of  the  main  hill  occupied  by  the  Rocky  Point 
booths;  conglomerate,  forming  the  eastern  part  of  this  hill,  and  a  solitary 
exposure  farther  northward,  and  then  various  sandstone  layers  as  far  east 
as  the  point,  the  intervening  courses  not  being  seen,  being  probably  some 
softer  shale.  The  strikes  of  the  exposures  at  Rocky  Point  are  N.  10°  W., 
dip  20°  E.  Many  of  the  pebbles  in  the  conglomerates  at  Rocky  Point  are 
of  considerable  size. 

A  short  distance  north  of  Sand  Point,  on  the  neck,  sandstone  and  con- 
glomerate are  exposed  dipping  to,vard  the  northwest.  At  the  southern  end 
of  Warwick  Neck,  near  the  light-house,  and  for  a  short  distance  westward, 
black  carbonaceous  shales  and  some  sandstones  are  exposed  dipping  in  gen- 
eral northward,  but  suggesting  in  places  a  sort  of  contortion  of  the  rocks  by 
a  force  acting  in  an  east-west  direction. 


CHAPTER   IV. 
THE  NORTHERN  SHORE  OF  THE  BAY. 

PROVIDENCK   RIVER   AISTD   EASTWARD. 

The  geology  of  the  area  directly  east  of  Warwick,  on  the  eastern  side 
of  Pi'ovidence  River,  in  Barrington,  is  laot  well  disclosed  by  outcrops. 

It  will  be  remembered  that  the  strike  of  the  exposures  west  of  Rocky 
Point  was  a  little  west  of  north  and  the  dip  low  east,  about  20°.  The 
strike  would  carry  these  rocks  a  little  west  of  Pawtuxet  village.  At  the 
mouth  of  the  Pawtuxet  River  sandstone  is  exposed,  and  the  neck  upon 
which  a  part  of  the  village  is  built  is  apparently  underlain  by  a  similar 
rock.  This  sandstone  could  easily  belong  to  the  Rocky  Point  series,  if  the 
Rocky  Point  exposures  be  correlated  with  the  exposures  on  the  eastern  side 
of  the  river. 

These  eastern  exposures  extend  from  East  Providence,  north  of 
Watchemoket  Cove,  along  the  shore  as  far  as  a  point  directly  west  of 
Riverside  Station.  This  section  is  chiefly  sandstone,  although  at  certain 
horizons  conglomerate  layers  are  abundant.  In  the  region  east  of  the 
Pomham  rocks  a  local  syncline  can  be  detected.  Immediately  east  of  this 
syncline  there  are  a  number  of  exposures  with  westerly  dip. 

Half  a  mile  east  of  the  Pomham  rocks  there  are  three  ridges  in 
obliquely  overlapping  order,  fi-om  south  to  north.  The  middle  ridge  shows 
a  westward  dip  of  30°.  The  middle  and  northern  ridges  contain  considera- 
ble conglomerate.  The  southern  ridge  consists  chiefly  of  sandstone. 
Isolated  exposures  occur  north  of  the  series  of  ridges.  No  perfectly 
satisfactory  stratification  planes  can  be  made  out  in  the  northern  and 
southern  ridges.  This  leaves  room,  of  course,  for  the  supposition  that  east- 
ward dips  may  occur  in  them  and  that  we  have  here  a  series  of  closely 
folded  anticlines  and  synclines. 


260  GEOLOGY  OF  THE  NARRAGAXSETT  BASIN. 

The  nearest  rocks  with  well-defined  dips  are  shown  in  a  set  of  large 
sandstone  exposures  a  moderate  distance  east  of  the  three  ridges  named. 
These  eastern  sandstone  exposures  show  an  undoubted  westward  dip  of 
40°  to  45°.  This  is  indicated  both  by  the  presence  of  conglomeratic  layers 
and  by  the  distribution  of  a  larg-e  number  of  plant  stems.  Owing  to  the 
two  distinct  cases  of  westward  dips  east  of  the  Pomham  local  syncline,  one 
in  the  middle  ridge,  the  other  in  the  sandstone  quarried  east  of  this  ridge, 
a  general  synclinal  structure, of  this  region  seems  a  possibility,  although 
the  probability  of  a  series  of  folds  here  must  not  be  excluded. 

With  this  possible  structure  in  view,  the  conglomerates  and  sandstones 
west  of  Rocky  Point  and  east  of  the  Pomham  rocks  are  correlated  as  belong- 
ing at  least  to  the  same  general  series,  above  the  rocks  found  farther  west- 
ward in  Warwick.  In  other  words,  these  rocks  are  believed  either  to  overlie 
the  Saunderstown  sandstone  series  as  a  distinct  superior  formation  or  to  form 
the  summit  of  that  series. 

If  this  be  true,  the  sandstones  and  conglomerates  east  of  the  Provi- 
dence River  must  dip  southeastward  on  approaching  Rumstick  Neck,  in 
order  to  underlie  the  exposures  south  of  that  neck,  if  the  shales  of  the  latter 
are  to  be  correlated  with  the  Aquidneck  series.  The  exposures  within  the 
writer's  field  are  inadequate  to  settle  this  question. 

EUMSTICK  NECK. 

The  first  exposures  eastward  of  Providence  River,  in  Barrington,  occur 
along  the  southeastern  shore  of  Rumstick  Neck.  About  a  quarter  of  a  mile 
west  of  the  southern  end  of  the  neck  lies  Long  Ledge,  made  up  of  Carbon- 
iferous sandstone  with  strike  N.-S.  and  dip  30°  E.  A  little  southeast 
the  same  sandstoiie  is  exposed  in  Riimstick  Rock  with  strike  of  E.-W. 
and  dip  45°  N.  The  sandstone  here  contains  impressions  of  plant  stems — 
one  like  calamites,  the  others  coarsely  ridged.  They  are  of  the  same 
type  as  those  found  at  Hills  Grove,  east  of  Providence  River,  north  and 
south  of  Silver  Spring,  in  the  quarry  east  of  the  range  of  three  ledges, 
northeast  of  Riverside,  and  elsewhere.  On  the  shore  itself  is  greenish  shale 
of  the  same  type  as  that  belonging  to  the  shale  series  northward.  It  seems 
to  have  a  strike  of  N.  20°  W.,  dip  30°  E.,  and  evidently  overlies  the  sand- 
stone of  the  ledges. 


CARBONIFEROUS  AREA  OF  BRISTOL  NECK.  261 

POPASQUASII  NECK. 

A  long  ridge  of  sandstone  lies  northwest  of  Ushers  Cove,  first  trending 
northward,  then  northeast,  and  then  more  northerly  again.  It  is  of  bluish 
color.  No  satisfactory  strikes  and  dips  could  be  determined,  although  the 
exposure  is  large. 

BRISTOL  :N^ECK. 

CARBONIFEROUS   AREA. 

The  lowest  Carboniferous  exposures  on  the  neck  consist  of  coaly 
black  shales,  opposite  the  Brothers  and  Deyers  Rock,  where  the  railway 
begins  to  turn  toward  the  southeast,  leaving  the  shore.  The  strike  seems 
to  be  N.  10°  W.,  dip  40°  E.  Species  of  Annularia  and  ferns  occur  in  the 
rock.  The  same  black  shales  are  found  three-foiu-ths  of  a  mile  farther  south- 
east, in  the  railway  cut,  where  the  strike  is  northwest  and  the  dip  aiortheast. 
Above  this  coaly  shale,  exposed  along  the  shore  a  quarter  of  a  mile  north 
of  the  Brothers,  lies  sandstone  containing  black  shaly  layers  showing  a 
strike  of  about  N.  10°  W.,  dip  40°  E.  Northeast  of  these  shore  exposures, 
east  of  the  railroad,  is  a  high  ridge  of  bluish  sandstone,  whose  strike  and 
dip  can  not  be  determined,  although  the  dip  is  probably  eastward  and  the 
strike  probably  of  such  a  character  as  to  connect  this  exposure  Avith  a  set 
of  sandstone  exposures  farther  south.  This  set  of  sandstone  exposures 
begins  on  the  hillside  east  of  the  Brothers  and  of  the  railroad.  It  strikes 
at  first  about  N.  20°  W.,  dipjDing  20°  E.  In  the  exposures  southeast  of 
this  locality  the  strike  becomes  more  and  more  nearly  east-west  until,  in  a 
quarry  just  west  of  the  Warren-Bristol  road,  it  is  about  N.  85°  W.,  with  a 
dip  of  20°  N.,  the  strike  becoming  perhaps  N.  80°  E.  just  before  reaching 
the  road. 

Above  this  sandstone,  toward  the  north,  lies  conglomerate.  The  most 
conspicuous  exposure  is  less  than  half  a  mile  south  of  Jacobs  Point,  just 
east  of  the  railroad.  The  conglomerate  liere  has  a  thickness  of  at  least  20 
feet.  Its  dip  is  low  eastward,  as  may  be  seen  by  sandstone  layers  near  its 
northern  end.  The  pebbles  are  of  sandstone  and  are  often  6  to  10  inches 
long.  The  other  conglomerate  exposiu-e  lies  1,500  feet  southward,  indicat- 
ing by  its  position  relative  to  the  other  exposure  a  strike  of  N.  10°  W.  It 
forms  a  small  knoll  in  an  open  field.     East  of  the  region  between  these  two 


262  GEOLOGY  OF  THE  NAREAGANSBTT  BASIN. 

conglomerate  exposures  lie  g-reeii  shales  of  the  same  type  as  those  belong- 
ing to  the  shale  series  southward.  The  green  shales  are  exposed  chiefly 
along  two  low  ridges,  the  first  one-third  of  the  distance  from  the  line  of 
the  conglomerates  to  the  Warren-Bristol  road,  and  the  second  about  two- 
thirds  of  that  distance.  No  strike  and  dip  could  be  determined.  The 
cleavage  is  mai'ked  and  the  planes  are  numerous.  Notwithstanding  the 
absence  of  definite  stratification  the  dip  is  undoubtedly  eastward,  corre- 
sj)onding  to  the  dip  and  strike  of  the  rocks  below  and  above.  The  green 
shales  therefore  here  overlie  a  very  coarse  conglomerate,  but  the  conglom- 
erate seems  to  have  had  but  a  very  limited  extension.  Overlying  the  bluish- 
green  sliale  is  a  bluish  sandstone  bed,  the  lowest  part  of  which  is  conglom- 
eratic, the  pebbles  beiag  of  small  size.  The  exposure  occurs  east  of  those 
last  mentioned,  east  of  the  Bristol-Warren  road,  and  forms  the  summit  of 
the  hill.  The  strike  can  not  be  well  determined,  but  seems  to  be  about 
N.  45'^  W.,  dip  45°  E.  Eastward  the  sandstone  becomes  rapidly  less  coarse, 
then  very  fine  grained,  and  is  finally  overlain  by  the  bluish  shale  which 
forms  the  exposures  over  the  remainder  of  the  area  of  the  neck  north  of 
the  pre-Carboniferous  granite  region.  This  shale  is  well  exposed  west  of 
the  road  half  a  mile  farther  northward,  east  of  the  road  in  the  valley,  and 
along  the  entire  western  margin  of  the  hill  just  beyond  for  half  a  mile 
southward.  It  is  also  exposed  near  the  summit  and  along  the  northern 
and  northeastern  sides  of  this  hill,  which  may  be  recognized  by  its  height 
of  120  feet,  as  indicated  on  the  map.  At  the  second  angle  of  the  road 
toward  the  northeast  of  the  hill  the  shale  is  very  black  and  carbonaceous. 
Farther  eastward,  east  of  another  main  north-south  road,  the  greenish-blue 
shale  is  again  abundantly  exposed  directly  east  of  the  summit  of  the  120- 
foot  hill.  The  shale  is  also  well  exposed  in  quarries  and  on  the  hillside 
less  than  a  mile  farther  northward  on  the  eastern  side  of  the  hill,  near  the 
top.  In  all  this  area,  excepting  in  the  cases  already  described,  the  Carbon- 
iferous is  represented  by  the  shale  series,  varying  from  bluish  green  to 
g-reenish  and  bluish,  sometimes  dark  blue  and  black. 

GRANITE    AREA. 

Granite  occupies  the  southern  part  of  Bristol  Neck.  A  coal  bed  was 
once  exposed  in  the  western  part  of  Bristol  only  a  few  feet  above  the 
harbor.     It  was  said  to  strike  east  of  north  and  to  dip  about  48°  W.     The 


GEANITE  ON  BRISTOL  NECK.  263 

coal  was  said  to  be  of  excellent  quality/  Grranite  is  exposed  at  the  north 
end  of  Walkers  Cove.  Thence  it  occurs  along  all  the  more  elevated  streets 
of  the  town.  North  of  Bristol  the  outcrops  extend  for  about  a  mile  a  little 
east  of  north,  and  then  east\'\'ard  for  another  mile.  The  nature  of  the  rock 
which  underlies  the  area  along  the  shore  east  of  the  very  large  quartz 
veins  on  the  east  side  of  Mount  Hope,  and  thence  northward  at  least  for  a 
mile,  is  unknown,  since  there  are  no  exposures.  At  Walkers  Cove,  and 
nmnerous  other  points  in  the  granite  area,  the  granite  is  coarsely  jDorphyritic, 
containing  phenocrysts  of  feldspar  an  inch  and  more  in  diameter.  Still 
more  frequently  it  does  not  contain  the  feldspar  phenocrysts.  Gneissoid 
structure,  in  consequence  of  shearing,  is  very  common,  the  shearing  having 
been  as  a  rule  in  the  direction  N.  30°  to  40°  W.  This  agrees  fairly  well  with 
the  direction  of  shearing  in  some  of  the  exposures  south  of  Common  Fence 
Point,  north  of  the  railroad,  on  Aquidneck  Island.  A  verj^  fine-grained 
pinkish  rock  occurs  in  places,  especially  in  the  valley  northwest  of  Mount 
Hope.  This  is  believed  to  be  an  aplitic  rock.  The  western  side  of  Mount 
Hope  is  formed  by  granite.  The  summit  and  precipitous  eastern  side  are 
formed  by  quartz  veins  of  gigantic  proportions,  varying  from  40  to  80  feet 
in  width.  Grranite  abuts  against  these  veins  on  the  west,  but  no  exposures 
occur  on  the  east.  On  the  shore  northwest  of  Mount  Hope  Point  a  black 
schistose  rock  is  included  in  the  granite.  Its  structure  is  probably  the 
result  of  shearing  in  the  granite. 

This  granite  may  have  formed  an  island  in  the  Carboniferous  sea,  but 
no  arkose  is  known  to  occur  at  any  point  on  Warwick  Neck,  and  no 
contacts  are  exposed  between  the  granite  and  any  clastic  rock.  Moreover, 
the  Carboniferous  shales  nearest  the  granite  area  do  not  show  either  strike 
or  dip,  and  the  cleavage  is  also  discordant  with  the  outline  of  the  granite 
area.  There  is,  therefore,  no  evidence  of  the  existence  of  the  granite  area 
as  an  island  in  Carboniferous  time,  although,  judging  from  the  history  of  a 
similar  granite  on  Conanicut,  south  of  Jamestown,  it  is  extremely  probable 
that  it  did  so  exist.  Moreover,  the  granite  of  the  Bristol  Neck  area  and  the 
pre-Carboniferous  granite  along  the  east  side  of  Taunton  and  Sakonnet 
rivers  show  features  so  similar  as  to  make  it  very  probable  that  they 
together  constitute  a  geological  unit. 


'  This  mine  has  been  filled  up.     Specimens  of  coal  shown  me  were  uf  the  same  nature  as  that 
from  the  Portsmouth  mine. — N.  S.  S. 


264  GEOLOGY  OF  THE  NAERAGANSETT  BASIN. 

WAEREX  IS^ECK. 

About  a  mile  north  of  Chases  Cove,  on  Kickamuit  River,  the  shore 
line  is  deeplj''  indented  and  a  valley  extends  thence  northward  for  about  a 
third  of  a  mile.  West  of  this  valley  are  abundant  exposures  of  conglom- 
erate, forming  two  hills  over  60  feet  high,  the  pebbles  being  rather  large, 
often  1  foot  in  length.  There  are  very  few  interbedded  sandstones,  and 
these  lie  almost  horizontal  or  dip  slightly  eastward.  The  northern  hill  lies 
southwest  of  the  angle  of  one  of  the  main  roads  of  the  neck.  Northeast 
of  this  angle  a  low  ridge  of  conglomerate  in  the  open  fields  continues  the 
exposures,  increasing  in  elevation  northward  on  entering  the  woodland. 
Two-fifths  of  a  mile  northeast  of  this  ridge,  along  the  railroad,  the  con- 
glomerate is  exposed  again,  showing  a  strike  of  N.  30°  W.,  dip  45°  E. 
Hardly  a  quarter  of  a  mile  eastward  the  conglomerate  has  a  strike  of  N. 
20°  W.,  dip  30°  E.  Between  these  two  exposures  southward,  in  the  fields, 
occur  others  with  approximately  the  same  strike  and  dip.  Farther  eastward, 
however,  the  fairly  abundant  exposures  along  the  south  side  of  the  railroad 
show,  eastward,  first,  a  northeast  strike  and  a  western  dip,  changing 
rapidly  to  an  almost  east-west  strike  and  a  northward  dip  of  perhajjs  20° 
to  30°. 

CONGLOMERATES  A:N^D   SHALES   OF   SWAKSEA   AND  WARREN,  NORTH 

OF  THE  NECKS. 

The  road  from  Coles  Station  to  Luthers  Corner  leads  first  northward, 
then  eastward,  and  tben  northward  again.  Just  south  of  the  second  angle 
of  the  road,  along  the  shore,  the  conglomerate  has  a  strike  of  about  N.  60°  E., 
dip  low  northward.  Northward  along  the  west  side  of  the  road  ai-e  several 
exposures,  the  most  southern  of  which  has  a  strike  of  about  N.  70°  E.,  dip 
about  50°  N.,  the  strikes  farther  north  being  also  decidedly  eastward  and 
the  dips  north.  East  of  these  exposures  a  road  leads  eastward  to  Fall  River. 
Where  it  crosses  Coles  River  there  are  exposures  on  both  banks.  Exposures 
also  border  both  sides  of  the  river  for  about  a  quarter  of  a  mile  northward; 
and  southward,  below  the  bridge,  exposures  are  found  in  the  channel  and 
on  the  west  bank.  The  strike  for  all  of  these  exposures  is  about  N.  45°  E., 
dip  20°  NW.  Along  the  road  leading  from  the  western  side  of  the 
bridge  northward  exposures  are  abundant  on  both  sides  of  the  road,  show- 


SWANSEA  AND  WAREEN.  265 

ing  in  general  a  northeast  strike  and  a  northwestern  clip.  One  of  the  more 
northern  exposures,  before  reaching  the  20-foot  contour  line,  indicating  a 
valley  entering  the  hillside  from  the  east,  shows  a  strike  of  N.  60°  E.,  dip 
45°  NW.  Continuing  on  this  road  northward,  and  tlien  following  the 
main  road  toward  Swansea  village,  there  are  abundant  exposures  of  the 
conglomerate  south  of  the  road,  not  far  beyond  the  mill  pond.  Here 
the  strike  is  about  N.  45°  E.,  dip  50°  NW.  About  a  third  of  a  mile  east- 
ward, at  some  distance  south  of  the  road,  the  strike  is  about  N.  50°  E., 
the  dip  northwest.  The  northwesterly  dip  is  shown  by  the  conglomerate 
exposures  at  various  points  north  of  Swansea  \dllage.  The  northeastern 
strike  and  northwestern  dip  is  also  shown  by  the  conglomerate  exposures 
which,  beginning  on  the  western  side  of  the  pond  southwest  of  the  village, 
reappear  on  the  eastern  side,  and  are  exposed  again  before  reaching  the 
main  street  of  the  village.  Following  the  road  east  from  Swansea  callage, 
and  taking  the  first  road  toward  the  north,  exposures  are  found  again  three 
quarters  of  a  mile  northward,  bordering  the  road  on  the  west.  The  same 
strikes  and  dips  can  still  be  recognized,  continuing  thence  northeastward  to 
Taunton  River. 

The  general  northeast  strikes  and  northwest  dips  from  the  first  exposure 
here  described,  northeast  of  Coles  Station,  along  Coles  Eiver,  throuo-h 
Swansea  Aallage,  show  conclusively  that  these  coarse  conglomerates  overlie 
the  sandstones  and  shales  farther  south  and  east. 

West  of  the  exposures  just  described,  from  Coles  Station  as  far  as  the 
mill  pond,  halfwa}^  between  Luthers  Corner  and  Swansea,  the  conglomer- 
ates dip  toward  the  east,  showing  a  synclinal  structure  over  this  area.  The 
easterly  and  northeasterly  dips  along  the  railroad,  half  a  mile  west  of  Coles 
Station,  have  already  been  mentioned.  A  little  west  of  north  of  Coles 
Station,  directly  west  of  the  first  strong  bend  of  the  road  already  described, 
conglomerate  is  exposed  at  the  margin  of  the  woods,  with  a  strike  of  about 
N.  65°  W.,  dip  about  30°  NE.  The  conglomerate  is  here  overlain  by 
sandstone  merging  into  a  fine-grained  shaly  rock.  Northeastward,  in  the 
fields,  the  conglomerate  strikes  N.  15°  W.,  and  dips  east.  West  of  Luthers 
Corner,  for  a  rather  long  distance  west  of  the  road  leading  north  from 
Coles  Station,  are  a  considerable  number  of  exposures,  most  abundant 
north  and  northwest  of  the  corner.  Their  strike  is  in  general  north-south, 
dip  eastward,  often  very  low.     Half  a  mile  north  of  the  bridge  across  Coles 


266  GEOLOGY  OF  THE  NAERAGANSETT  BASIN. 

River,  west  of  the  road,  and  uortli  of  tlie  20-foot-contour  valley  already 
noted,  are  a  number  of  exj)osures  showing  in  general  a  strike  of  about 
N.  20°  E.,  dij)  45°  E.  Overlying  some  of  the  more  southeastern  of  these 
exposures,  on  the  west  side  of  the  road,  is  a  bluish  shale.  The  conglomerate 
is  also  exposed  east  of  the  road.  A  third  of  a  mile  west  of  the  mill  pond  a 
long  exposure  beside  the  road  west  of  the  bend  shows  a  strike  of  N.  25°  E., 
dip  30°  SE.  Overlying  the  conglomerate  is  a  greenish  shale.  Just  west 
of  the  mill  pond  the  strike  is  N.  70°  E.,  and  the  dip  almost  veiiical. 
Northeast  of  the  mill  pond  the  conglomerate  exposures  northwest  of  Levins 
Brook  do  not  vary  far  from  the  horizontal,  and  the  synclinal  structure  can 
no  longer  be  followed. 

The  detection  of  the  synclinal  structure  between  Coles  Station  and 
the  mill  pond,  and  the  more  horizontal  position  of  the  rocks  to  the  north- 
ward, is  of  some  assistance  in  establishing  the  continuity  of  this  more 
eastern  conglomerate,  whose  stratigrapliical  equivalents  with  the  conglom- 
erates in  Warren,  north  of  Bristol  Neck,  and  in  adjacent  parts  of  Swansea, 
can  be  easily  determined.  Indirectly  also  it  is  serviceable  in  determining 
the  position  of  the  bluish-green  shale  series  of  Bristol  Neck,  as  the  following- 
notes  may  show : 

The  wide  distribution  of  the  bluish-green  shale  series  in  Bristol  Neck 
has  already  been  noted.  From  Warren,  eastward  along  the  first  road  lead- 
ing north,  passing  east  of  Belchers  Cove  and  Warren  River,  bluish  shale 
occurs  east  of  the  road  a  third  of  a  mile  south  of  Kings  Rock.  Sandstone 
occurs  Avest  of  the  road,  and  is  also  exposed  in  the  northeast  angle  of  the 
first  road  leading  toward  the  east.  At  the  latter  locality  a  few  stray  peb- 
bles of  large  size  are  embedded  in  the  sandstone.  At  Kings  Rock,  west 
of  the  road,  on  the  Massachusetts-Rhode  Island  boundary  line,  and  also 
northeastward,  east  of  the  road,  are  large  exposures  of  the  bluish  shale. 
The  strike  of  these  rocks  is  about  N.  15°  E.  A  mile  south  of  Kings 
Rock  a  road  leads  off  eastward  to  Luthers  Corner.  Less  than  half  a  mile 
along  this  road  another  branches  off  northward.  South  of  this  point  a 
considerable  area  is  covered  by  bluish  and  greenish  shales,  frequently 
exposed.  These  shales  are  also  exposed  on  the  eastern  side  of  the  hill,  east 
of  the  road,  at  several  points  from  a  quarter  of  a  mile  north  of  the  road 
corner  to  half  a  mile  northward,  and  they  are  found  again  a  mile  north  of 
the  road  corner,  a  quarter  of  a  mile  east  of  the  road,  near  the  State  boundary 


GAEDENBRS  NECK.  267 

line.  This. set  of  exposures  indicates  a  strike  of  N.  15°  E.  East  of  the 
last  exposure  is  coarse  sandstone.  Toward  the  northwest  and  north  extend 
several  ridges  of  sandstone  and  conglomerate,  the  most  eastern  of  which 
can  be  followed  for  a  mile,  as  far  as  the  next  east-west  road.  The  strike 
is  N.  15°  E.,  dip  always  eastward,  often  as  low  as  20°.  Conglomerate 
and  sandstone  also  occur  north  of  a  house  some  distance  east  of  the  road,  a 
quarter  of  a  mile  south  of  the  State  boundar}^  line.  A  mile  northeast  of 
Kings  Rock  numerous  exposures  border  the  roads  eastward  and  northward. 
They  consist  chiefly  of  sandstone  and  some  conglomerate,  dipping  eastward, 
but  they  also  contain  greenish  shaly  laj^ers  toward  the  north  end  of  the 
series  of  exposures,  where  the  strike  seems  to  be  more  nearly  east-west  and 
the  dip  southward. 

A  third  range  of  bluish  shales  forms  a  ridge  bearing  N.  15°  E.,  both 
north  and  south  of  the  road  to  Luthers  Corner,  already  mentioned.  East- 
ward from  this  ridge,  three-quarters  of  a  mile  northward  along  the  first 
road  on  the  east  side,  conglomerate  is  exposed;  strike  N.-S.,  dip  70°  E. 
Greenish  shale  miderlies  it  on  the  west. 

The  various  exposures  north  of  Bristol  Neck,  just  described,  seem  to 
indicate  that  the  bluish-green  shales  underlie  the  great  mass  of  conglom- 
erates. These  conglomerates  are  the  coarse  conglomerates  on  Aquidneck 
Island  and  occur  at  a  considerable  distance  above  the  lowest  beds  of  the 
Carboniferous  exposed  along  the  eastern  shore  line  of  the  basin,  from 
Steep  Brook  to  Tiverton. 

GARDENERS   NECK, 

The  eastern  line  of  outcrops  of  the  coarse  conglomerate  runs  through 
Swansea  village,  in  a  northeasterly  direction.  Beneath  these  conglomerates, 
on  the  east,  occurs  a  series  of  shales  and  sandstones.  South  of  the  pond 
southwest  of  Swansea  village,  in  the  bed  of  the  creek  which  forms  its 
outlet,  and  in  the  field  between  the  creek  and  the  road,  there  are  several 
exposures,  chiefly  sandstone,  but  also  some  more  shaly  courses,  dark 
blue  in  color.  Southward  rather  more  than  a  mile,  on  the  road  to  South 
Swansea,  an  exposure  of  coaly  shale  occurs  south  of  the  road  leading 
eastward  to  Fall  River.  This  exposure  occurs  in  a  digging-  on  the  eastern 
side  of  the  Neck,  near  the  top  of  the  hill.  Half  a  mile  farther  south,  near 
the  base  of  the  hill,  toward   Lees  River,  a  shaly  sandstone  or  slaty  rock 


268  GEOLOGY  OF  THE  NAERAGAlSrSETT  BASIN. 

occiTi'S.  Its  strike  is  probably  N.  40°  to  45°  E.;  this  at  least  is  the  direction 
of  the  line  of  outcrop.  The  color  is  bluish  black,  or  quite  black  where 
shaly.  This  more  southern  set  of  exposures  occurs  stratig-raphically 
beneath  the  coaly  shale  lying  farther  north. 

BRAYTONS   POIISTT  AND  NORTHWARD. 

On  the  northwestern  side  of  the  point  black  coaly  shales  are  exposed. 
These  continue  southward  as  far  as  the  middle  of  the  west  shore,  where 
sandstone  is  frequentl}^  interbedded.  The  strike  farther  north  seems  to  be 
N.  50°  E.,  but  southward  it  varies  to  N.  70°  E.,  and  becomes  N.  30°  E.,  dip 
70°  W.,  near  the  middle  of  the  west  shore.  The  black  shales  here  con- 
tain Annularia  longifolia  and  fern  impressions.  Farther  southward  black 
coaly  shales  continue  to  be  exposed  as  far  as  the  southern  end  of  the  point 
and  its  southeastern  side.  These  more  southern  exposures  show,  a  strike  of 
N.  50°  E.,  dip  80°  W.,  or  other  variable  lower  angles.  The  bedding  here  is 
not  often  well  shown. 

SEWAMMOCK  KECK. 

A  mile  and  a  quarter  west  of  Brayton,  on  the  road  from  Fall  River, 
crossing  the  neck,  on  the  western  side  of  the  hill,  a  rather  coarse  sandstone 
is  well  exposed.  Its  real  strike  and  dip  could  not  be  determined,  the 
apparent  bedding  being  probably  only  cleavage.  Similar  gra}^  sandstone  is 
exposed  half  a  mile  west  of  Pottersville,  north  of  the  road.  This  sandstone 
probably  underlies  the  coaly  shales  of  Braytons  Point. 


CHAPTER    V. 
THE  EASTERN  SHORE  OF  THE  BAY. 

STEEP  BROOK. 

Pre-Carboniferous  granite  forms  the  steep  slopes  of  the  hilly  country- 
bordering  Taunton  River  on  the  east.  The  western  line  of  outcrop  of  tlie 
granite  extends  from  Steep  Brook  northward  as  far  as  the  point  where  the 
Myrick  branch  of  the  railroad  leaves  the  main  line.  The  line  of  outcrop 
of  the  granite  then  turns  abruptly  eastward  and  follows  the  southern  side  of 
the  railroad  as  far  as  Washington  Mountain.  At  Steep  Brook  the  granite 
is  well  exposed  along  the  sides  and  in  tlie  bed  of  the  brook.  The  contact 
with  the  Carboniferous  rocks  is  not  exposed.  The  lowest  exposure  of  clastic 
rock  consists  of  conglomerate,  strike  N.  45°  E.,  dip  30°  W.  Toward  the 
north,  overlying  the  conglomerate,  is  sandstone,  with  a  dip  of  40°  W. 
Thirty  feet  west  of  the  conglomerate  there  was  not  long  ago  exposed  a 
narrow  coal  seam,  with  coaly  slate  containing  fern  impressions.  Its  strike 
was  N.  15°  E.,  dip  20°  W.  West  of  the  coaly  layer  occurs  a  considerable 
thickness  of  arkose,  in  some  places  scarcely  showing  bedding,  in  others 
indicating  the  planes  of  bedding  by  color  banding  caused  by  more  carbo- 
naceous material  in  certain  thin  layers.  A  little  of  the  arkose  material 
exists  beneath  the  coaly  layer.  The  arkose  consists  chiefly  of  quartz, 
derived  from  decayed  granite.  The  quartz  grains  as  a  rule  are  not  rounded. 
The  granite  which  furnished  the  constituents  of  the  arkose  must  have  been 
reduced  to  a  mass  of  loose  material  by  aerial  decomposition,  so  that  the 
quartz  grains  were  readily  washed  away  in  order  to  form  the  arkose,  while 
the  feldspathic  material  formed  interbedded  layers  of  the  impure  kaolin, 
which  was  once  quarried  by  the  owner  of  the  premises  for  shipment  to 
pottery  works.  The  absence  of  the  arkose  and  clay  material  near  the  base 
of  the  series  here  is  noteworthy.  Still  more  important  is  the  conglomerate 
layer  near  the  base,  for  the  conglomerate,  although  so  near  the  granite 
area,  does  not  consist  of  granite  pebbles,  but  of  quartzitic  pebbles,  often  3 

269 


270  GEOLOGY  OF  THE  NARRAGANSETT  BASIN. 

iuches  long,  similar  in  character  to  the  pebbles  in  the  Dighton  conglomerate. 
The  granite  from  which  the  arkose  and  kaolin  were  derived  was  too  decayed 
to  furnish  pebbles,  but  the  quartzitic  rocks  withstood  weathering  sufficiently 
to  furnish  good  pebbles  to  the  basal  conglomerates,  in  spite  of  probably 
long  transportation. 

FALL   RIVER. 

A  still  more  interesting  exposure  occurs  in  Fall  River,  in  Annawan 
street,  halfway  down  the  hillside,  behind  some  mills.  The  eastern  border 
of  the  present  Carboniferous  area  extends  from  Steep  Brook  along  the 
escarpment  bordering  Taunton  River  to  this  locality  in  Fall  River,  with  a 
trend  of  about  N.  32°  E.;  southward  to  Townsend  Hill  its  trend  is  N,  40°  E.' 
In  the  angle  a  considerable  exposure  of  the  overlying  Carboniferous  rocks 
is  preserved.  Behind  the  mill  on  Annawan  street  the  arkose  rests  directly 
upon  the  granite  or  is  separated  from  it  only  by  a  thin  course  of  coaly 
shale.  The  contact  is  well  shown.  Arkose  layers,  composed  chiefly  of 
angular  quartz  grains  derived  from  the  granite,  alternate  with  coaly  shale 
layers.  Northward  toward  the  railway  tunnel  under  the  next  street,  the 
alternation  of  arkose  and  coaly  shale  layers  continues,  the  arkose  changing 
to  a  gritty  sandstone;  the  coaly  slate  then  forms  a  considerable  exposure, 
overlying  the  arkoses,  and  constituting  the  steep  wall  of  the  hillside  as  far 
as  the  railway  track;  strike  N.  50°  E.,  dip  40°  W.;  farther  south,  strike 
N.  30°  E.  Fern  impressions  occur  in  the  shales.  West  of  the  railway  track 
occurs  a  gritty  sandstone. 

TOWNSEND   HILL. 

Two  and  three-fourths  miles  southwest  of  the  exposure  in  Fall  River 
occurs  the  exposure  on  the  west  side  of  Townsend  Hill.  Granite  forms 
the  hillside  down  to  the  100-foot  contour.  Below,  where  a  small  bench 
occurs,  forming  a  northerly  projection  on  the  hillside,  the  arkose  is  exposed. 
The  actual  contact  with  the  underlying  granite  is  not  seen,  the  stratigraphic 
interval  being  about  5  feet. 

'  The  existing  escarpment  seems  to  me  to  be  due  to  tlie  deformation  of  tlie  granite  formation  of 
the  basin  and  the  subsequent  removal  of  the  softer  stratified  beds.  If  the  Carboniferous  shore  lay 
along  this  line,  it  was  there  but  for  a  short  time  during  the  progressive  overlapping  of  the  accumu- 
lating basal  sediment. — N.  S.  S. 


EASTERN  SHOEE  OF  THE  BAY.  271 


TI^TERTOiS^. 


The  granite  escarpment  trends  N.  30°  E.  as  far  as  the  western  side  of 
Pocasset  Hill,  changing  thence  to  N.  13°  E.  as  far  as  the  exposures  north- 
east of  the  railroad  bridge.  The  lowest  exposures  of  the  Carboniferous 
series  occur  in  the  quarry  on  the  hillside.  Here  the  prevailing  rock  is 
arkose.  The  lowest  part  of  this  arkose,  stratigraphically,  occurs  very  near 
the  granite.  Nearer  the  lower  end  of  the  quarry  blackish  shale  occurs. 
Tracing  the  exposures  northward,  a  whitish,  fine-grained,  quartzitic  rock, 
very  much  like  the  rock  exposed  west  of  East  Greenwich,  occurs  between 
the  Carboniferous  rock  and  the  granite,  and  is  evidently  pre-Carboniferous. 
Along  the  railroad  tracks,  overlying  the  grits,  occur  abundant  exposures  of 
conglomerate,  composed  chiefly  of  quartzose  pebbles,  some  of  them  8 
inches  long.  No  granite  pebbles  were  seen.  Coarse  sandstones  are  inter- 
bedded.  The  abundance  of  quartzose  pebbles  and  the  absence  of  granite 
pebbles  here  is  paralleled  at  Steep  Brook.  The  more  northern  exposures 
along  the  railroad  have  a  strike  N.-S.  and  dip  30°  W.  At  the  quarry  the 
strike  becomes  N.  35°  E.,  the  dip  40°  W. 

The  next  exposure  of  Carboniferous  rocks  occurs  a  mile  and  tliree- 
quarters  farther  south,  east  of  the  northern  end  of  Nannaquacket  Pond. 
At  the  northern  end  of -the  pond  the  granite  appears  at  the  shore.  But  a 
short  distance  farther  south,  on  the  hillside,  the  arkose  is  seen  resting  upon 
the  granite.  A  little  coaly  shale  is  interbedded  with  the  arkose.  Strike 
N.  20°  W.,  dip  45°  W.  Farther  south  the  granite  comes  down  to  the  road- 
side. It  is  evident  that  the  contact  line  between  the  Carboniferous  rocks 
and  the  granite  must  turn  westward  where  Sin  and  Flesh  Bi-ook  enters  the 
pond.  Granite  occurs  also  along  the  northern  side  of  Sin  and  Flesh  Brook 
near  the  pond,  and  also  directly  north  of  the  pond,  on  the  north  side  of  the 
road  skirting  the  same.  This  would  require  a  still  farther  westward  trend 
of  the  shore  line. 

Returning  to  the  arkose  exposure,  the  granite  comes  down  to  the  road 
near  the  fork  of  the  way.  North  of  the  road,  after  passing  the  turn  toward 
the  east,  the  arkose  occurs  again  high  up  on  the  hillside,  but  associated  with 
considerable  coaly  shale.  The  strike  here  is  N.  85°  W.,  dip  65°  to  70°  S. 
If  the  observer  crosses  the  road  at  its  bend,  he  will  find  an  excellent  exposure 
in  the  open  area  on  the  hillside,  southwest  of  the  wooded  summit.     Here  the 


272  GEOLOGY  OF  THE  >f AEEAGANSETT  BASI^. 

contact  between  tlie  granite  and  the  overlying  Carboniferous  rocks  is  again 
well  shown.  The  clastic  rocks  consist  of  a  series  of  interbedded  arkoses  and 
coaly  shales,  soraetimes  one,  sometimes  the  other  kind  of  rock  forming  the 
contact  with  the  granite.  The  contact  line  is  usually  very  distinct.  The 
same  strike  of  N.  85°  W.,  dip  60°  S.,  is  shown.  The  arkose  and  granite  con- 
tact can  be  followed  as  far  as  the  creek  entering  Nannaquacket  Pond  from  the 
east.  From  the  pond  southward  it  evidently  takes  a  more  southerly  course, 
following  the  eastern  side  of  the  low  land  west  of  the  granite  hill,  and  then 
following  the  valley  of  a  small  brook  as  far  as  Tiverton  Four  Corners. 

North  of  Nannaquacket  Pond  normal  granite  occurs,  as  already  de- 
scribed. Still  farther  north  a  white  fine-grained  micaceous  schist  is 
exposed  over  a  considerable  area,  until  farther  northward  the  granite 
appears  again.  The  whitish  micaceous  schist  may  be  followed  eastward 
across  the  north-south  road.  It  forms  the  southern  end  of  the  hill  north 
of  Sin  and  Flesh  Brook  and  occurs  along  the  northern  branch  of  the 
stream.  It  also  occurs  south  of  the  brook,  the  line  of  contact  with  the 
granite  crossing  south  of  the  ice-house  pond.  West  of  this  pond,  along 
the  road,  the  schist  has  been  brecciated  so  as  to  resemble  at  first  sight  a 
cong'lomerate.  In  places  this  rock  looks  very  much  like  a  very  fine-grained 
aplite  made  schistose  by  shearing.  East  of  the  ice  house,  between  the 
branches  of  the  brook  and  also  south  of  the  south  branch,  a  greenish  schist, 
often  containing  a  dark-greenish  hornblendic-looking  mineral,  is  common. 
The  granite  nortli  of  this  schist  area  not  uncommonly  also  shows  the  effect 
of  shearing  and  has  a  sort  of  gneissoid  structure.  The  schist  area  has  not 
been  thoroughly  studied.  This  will  later,  however,  be  desirable  in  order 
to  learn  whether  the  present  eastern  border  of  the  Carboniferous  area  north 
of  Nannaquacket  Pond  is  due  to  the  topography  of  the  early  Carboniferous 
sea  bottom  or  is  a  result  of  subsequent  sliding  of  the  more  northern  pre- 
Carboniferous  granite  to  the  westward. 

GOULD  ISLAND. 

The  main  mass  of  the  island  consists  of  a  very  fine-grained  rock,  vary- 
ing in  color.  In  some  places  it  is  white,  with  minute  black  specks,  prob- 
ably biotite;  in  others  it  is  light  bluish  gray  or  dark  blue;  in  still  others  it 
is  gray,  but  contains  many  light-colored  blotches.  This  rock  has  been 
extensively  brecciated  by  a  shearing  action  which  took  place  in  a  direction 


GRANITE  OP  NORTHEEN  AQUIDNECK.  273 

about  N.-S.,  or  a  little  west  of  north.  In  consequence  of  the  breccia- 
tion  the  rock  often  has  a  decidedly  conglomeratic  appearance.  Where 
shearing  has  taken  place  the  pebble-like  fragments  usually  remain  light  in 
color  and  the  cementing  material  is  darker.  In  other  places  the  fragments 
are  very  dark  in  color  and  seem  macroscopically  to  be  full  of  hornblende 
and  black  mica.  These  dark  fragments  resemble  closely  the  so-called  dark 
or  hornblendic  schists  of  the  Sin  and  Flesh  Brook  section,  while  the  light- 
colored  rocks  resemble  the  lighter  so-called  quartzitic  schists  of  that  section. 
A  pinkish  aplite  cuts  the  rock  near  the  southeast  end  of  Gould  Island  in 
the  form  of  narrow  dikes. 

GRAKITE    AREA    OF    THE    KORTHEAST    EKD    OF    AQUIDNECK 

ISLANB. 

Whitish  granite  occurs  along  the  southern  margin  of  Hummock  Point, 
and  reddish  granite  is  found  along  the  east  shore  farther  north.  A  pinkish 
aplite  cuts  the  same.  Whitish  granite  forms  a  hill  extending  north  of 
Hummock  Point  as  far  as  the  railroad.  The  granite  is  frequently  sheared 
in  a  north-south  direction,  the  result  varying  from  a  gneissoid  granite 
to  a  black  mica-schist.  Half  a  mile  north  of  the  railroad  another  set  of 
ridges  begins,  extending  northward.  It  consists  of  whitish  granite,  sheared 
in  a  direction  west  of  north,  often  N.  20°  W.  One  result  of  the  shearing 
is  again  a  gneissoid  structure,  varying  to  a  black  mica-schist.  Associated 
with  the  granite  toward  the  middle  and  northward  is  the  fine-grained 
quartzitic  rock  already  described  as  occurring  with  the  granite  northeast 
of  the  railroad  bridge  at  Tiverton,  and  also  as  occurring  in  the  Sin  and 
Flesh  Brook  exposures.  Some  of  the  Gould  Island  rock  is  also  very 
similar  in  character  to  the  whitish  rock  at  the  northeast  end  of  Aquidneck 
Island,  the  whiter  rock  being  probably  identical  in  the  two  places.  At 
Common  Fence  Point  occurs  a  reddish  granite,  not  gneissoid. 

The  rocks  exposed  from  Gould  Island  to  Common  Fence  Point  are 
evidently  pre-Carboniferous,  and  belong  to  the  same  series  as  the  Sin  and 
Flesh  Brook  exposures,  and  that  northeast  of  the  Tiverton  railroad  bridge 
on  the  hillside.  The  Carboniferous  exposures  on  the  hillside  northeast  of 
Tiverton  are  noteworthy,  suggesting  that  the  eastern  border  of  the  Carbon- 
iferous  area   extends   southward  toward  the  stone  bridge.     Possibly  this 

MON  XXXIII 18 


274  GEOLOGY  OF  THE  NAEEAGANSETT  BASIN. 

border  passes  southward  from  the  stone  bridg-e,  rounds  the  granites  and 
schists  north  of  Nannaquacket  Point,  and  then  continues  southward,  east  of 
the  pond.  In  that  case  the  pre-Carboniferous  range  of  exposures  between 
Gould  Island  and  Common  Fence  Point  miist  have  been  brought  to  their 
present  position  hj  means  of  a  fault  bringing  up  these  rocks  from  below. 
At  least  there  is  no  evidence  that  the  Gould  Island-Common  Fence  Point 
range  of  exposures  formed  an  island  in  the  Carboniferous  seas. 

This  explanation  makes  it  unnecessary  to  hypothesize  any  connection 
between  the  Common  Fence  Point  range  of  granites  and  the  Bristol  Neck 
granite  area  above  the  water  surface  in  Cai'boniferous  times. 

EASTEKK    BORDER     OF    THE    CARBOXIEEROITS    BASI?^    SOUTH    OF 
TIVERTOX  FOUR   CORKERS. 

Half  a  mile  south  <_^f  Tiverton  Four  Corners  granite  is  exposed  on  the 
northwest  side  of  the  hill,  south  of  the  brook  entering  Nonquit  Pond  from 
the  east.  The  granite  continues  to  be  exposed  southward  for  a  short  dis- 
tance, when  greenish  rock,  having  the  appearance  of  a  very  fine-grained 
sandstone,  occurs.  Its  schistosity  is  N.  40°  E.,  dip  45°  SE.,  and  there  is  a 
probability  that  this  should  be  taken  as  the  strike  and  dip  of  the  bedding. 
This  rock  is  exposed  along  the  apparent  strike  at  a  number  of  places  on  the 
northwest  side  of  the  hill.  A  quarter  of  a  mile  southeast,  along  the  road- 
side, the  granite  is  abundantly  exposed.  The  granite  has  been  sheared  so 
as  to  present  a  pseudo-gneissoid  structure  with  a  northeasterly  strike.  The 
granite  and  the  fine-grained  rock  are  pre-Carboniferous.  The  eastern  border 
of  the  Carboniferous  area  probably  extends  from  Tiverton  Four  Corners 
east  of  Nonquit  Pond  and  Avest  of  the  granite  hill  southward. 

The  granite  is  well  exposed  along  the  southern  end  of  the  hill  north- 
east of  Tiverton  Four  Corners,  almost  east  of  the  church  north  of  Tiverton. 
On  the  east  side  of  Borden  Brook  the  granite  has  been  considerably  sheared 
in  a  direction  about  N.  30°  E.  The  granite  of  this  region  contains  in 
places  abundant  phenocrysts  of  feldspar  from  1  to  2  inches  in  diameter,  and 
these  have  been  sheared  to  a  lenticular  form,  producing  a  sort  of  augen- 
gneiss.  Where  the  shearing  was  more  marked  the  black  mica  increased  in 
quantity.  Extreme  shearing  reduced  the  granite  in  places  to  a  biotitic 
schist,  whose  real  character  it  is  not  possible  to  recognize  in  the  case  of 
every  exposure.     Gradations  from  one  into  the  other  can,  however,  be  found. 


JSrONQUIT  POND  TO  WINDMILL  HILL.  275 

The  hill  east  and  north  of  Pachet  Brook  also  shows  abundant  granite 
exposures  along  the  southern  and  eastern  sides  of  the  elevation.  On  the 
southeastern  side  it  includes,  in  several  places,  large  fragments  of  rock, 
ha\ang  in  some  places  the  structure  of  a  biotitic  fine-grained  schist 
of  blackish  color,  in  others  that  of  a  ver}^  fine-grained  whitish  rock, 
mottled,  when  broken  across  the  schistosity,  with  blackish  specks  caused 
hj  biotite  flakes.  These  included  schist  masses  are  distributed  along  a 
line  N.  30°  E.  in  an  irregular  manner.  They  present  the  same  strike  in 
their  schistosity,  and  dip  about  60°  to  70°  E.  It  would  seem,  therefore, 
that  they  once  formed  a  connected  series  in  this  region.  It  would  be 
interesting  to  learn  whether  these  schists  bear  any  close  relation  to  the 
Little  Compton  shales  farther  south,  but  the}'  probably  preceded  them. 
The  granite  near  these  schists  is  often  porphyritic  with  large  phenocrj'sts 
of  feldspar.  This  is  also  true  of  the  nearest  exposure  of  granite  east  of  the  ' 
north  branch  of  the  brook.  Farther  eastward  the  granite  is  of  the  ordinary 
type.  Southward,  west  of  the  south  branch  of  the  brook,  at  various  points 
near  the  road,  a  whitish  granite  is  exposed.  Farther  westward  there  is  no 
exposure  of  any  kind  for  almost  half  a  mile,  imtil  the  Little  Compton 
shale  outcrops  are  reached.  The  line  of  western  outcrop  of  the  granite 
must  therefore  pass  somewhere  between  these  regions  in  a  southeasterly 
direction.  It  probably  extends  west  of  the  road  leading  north  from  Little 
Compton;  1^  miles  south  of  Little  Compton  post-office  it  is  known  to  turn 
toward  the  southwest,  reaching  Sakonnet  River,  south  of  Churchs  Cove, 
about  a  mile  north  of  the  breakwater.  The  granites  from  here  south  to  the 
point  are  often  coarsely  porphyritic. 

SAlSTDSTOlSrE  SERIES  BETWEEN  WINDMILE  HIEE  AISTD  THE  COVE 
NORTH  OF  BROWNS  POINT. 

South  of  the  mouth  of  the  outlet  of  Nonquit  Pond  coaly  shales  are 
exposed  along  the  shore,  bordering  the  same  for  about  700  feet.  Then 
sandstone  occurs  on  the  west  of  the  shales,  showing  fine  cross  bedding,  made 
distinct  by  thin  layers  containing  more  carbonaceous  material.  The  general 
strike  is  parallel  to  tlie  shore,  or  N.  20°  E.,  dip  45°  to  65°  W.  Farther  south 
an  inward  bend  of  the  shore  exposes  the  coaly  shale  again.  These  shales 
contain  indistinct  leaf  impressions  of  unknown  affinities,  and  traces  of  ferns 
can  still  be  found.     Farther  south  there  is  more  sandstone,  but  here  east  of 


276  GEOLOGY  OF  THE  NARRAGANSETT  BASIX. 

the  coaly  shale,  and  dipping  45°  E.  If  this  indicates  an  anticline,  it  is 
evidently  a  sharp  one,  and  the  folding  has  been  obscured  in  the  shales  by 
abundant  cleavage  in  several  directions.  It  is  also  a  long  fold,  extending 
from  the  most  northern  shale  exposure  for  at  least  half  a  mile  southward. 
The  sandstone,  dipjDing  east,  at  the  north  has  a  strike  of  about  N.  5°  E., 
following  the  shore  for  a  considerable  distance,  and  at  the  south  end  the 
strike  changes  to  N.  30°  E.,  the  dip  being  50°  SE.  Beyond  this  is  a  fault 
having'  the  same  trend  of  N.  30°  E. 

In  some  places  the  sandstone  is  very  coarse  and  contains  a  great 
number  of  small  pebbles.  Toward  the  fault  the  sandstone  is  often  very 
quartzitic,  somewhat  resembling  the  arkose  along  the  shore,  but  the  quartz 
grains  are  as  a  rule  much  smaller  in  size.  South  of  the  fault  line  the  shore 
is  bordered  by  sandstone,  often  coarse,  or  filled  with  small  pebbles;  less 
frequently  it  is  decidedly  conglomeratic,  with  much  stretched  pebbles.  Just 
south  of  the  fault  a  fine  conglomerate  bed  was  once  overlain  by  black  shale, 
small  patches  of  which  are  still  scattered  over  its  surface,  indicating  a 
general  southerly  dip  of  about  20°. '  Farther  south  the  strike  is  N.  70°  W., 
dip  25°  S.,  but  there  is  also  evidence  of  cross  beddi'ng,  suggesting  shallower 
water  eastward.  Near  the  most  western  extension  of  the  shore  a  long 
plant  stem  is  exposed  for  several  feet  in  the  coarse  sandstone,  but  shearing 
makes  it  impossible  to  identify  it.  Small  plant  stems  occur  near  by,  resem- 
bling the  Silver  Spring  plant  stems.  Farther  south,  at  the  western  termina- 
tion of  the  Alray  Farm  road  to  the  shore,  the  coarse  sandstone,  containing 
numerous  fine  pebbles,  shows  a  strike  of  N.  60°  W.,  dip  20°  SW.,  indicated 
by  numerous  patches  of  coaly  shale,  which  cover  its  surface  and  which 
once  were  connected  and  formed  a  continuous  layer. 

Southward  from  this  region  the  bedding  is  often  difficult  to  follow  for 
anv  considerable  distance.  Not  infrequently  the  stiike  is  nearly  east- west, 
and  the  dip  is  then  southerly,  usually  about  20°.  But  at  many  points  along 
the  shore  there  is  bedding  striking  more  nearly  parallel  to  the  shore  and 
dipping  westward,  often  very  steeply.  In  some  cases,  especially  where  the 
dip  is  very  steep,  this  west  dip  seems  to  be  partly  due  to  folding  caused  by 
pressure  transverse  to  the  trend  of  the  border  of  the  basin.  Frequently, 
however,  it  is  accompanied  by  distinct  evidences  of  cross  bedding.  In  such 
cases  a  steep  westward  dip  not  infrequentl}^  curves  westward  so  as  to  reach 


SANDSTONES  NORTH  OF  BROWNS  POINT.  277 

an  almost  horizontal  position.  At  some  localities  a  general  study  of  the 
rock  indicates  that  more  or  less  horizontal  beds  wei'e  repeatedly  attacked 
on  the  west  side  by  waves.  The  westward-sloping  cut-out  margins  of  these 
beds  were  later  covered  by  similar  sand  beds,  which  were  themselves  nearly 
horizontal.  This  whole  series  at  present  dips  in  a  general  way  southward 
at  an  angle  of  about  20°.  Toward  the  south  the  strike  seems  to  be  more 
nearly  N.  60°  E.,  dip  45°  E.,  the  dip  decreasing  rapidly  southward  until  it 
becomes  only  about  10°.  Tt  is  difficult  to  determine  the  real  strike  of  the 
more  southern  shore  outcrops. 

North  of  the  fault  line  mentioned  above,  the  sandstone  rarely  contains 
pebbles  over  an  inch  long.  Southward  for  some  distance  there  are  distinct 
conglomerate  layers.  The  pebbles  usually  do  net  exceed  3  inches  in 
length,  although  some  beds  show  pebbles  somewhat  longer,  considerably 
stretched.  Granite  pebbles  are  not  infrequent,  but  are  hardly  recognizable 
on  account  of  the  extreme  shearing. 

A  very  coarse  conglomerate,  some  of  the  pebbles  a  foot  in  length, 
occurs  along  the  farm  road  west  of  the  house  on  the  west  side  of  Windmill 
Hill.  Many  of  these  pebbles  are  composed  of  quartzite  and  are  of  much 
larger  size  than  the  pebbles  in  the  exposures  along  the  bank  farther  south. 
They  occur  between  the  60-foot  and  80-foot  levels. 

Nothing  is  known  of  the  stratigraphic  position  of  these  rocks.  The 
following  remarks,  however,  may  be  pertinent.  The  present  eastern  mar- 
gin of  the  Carboniferous  basin,  as  a  rule,  shows  arkose  and  coaly  shales  as 
the  basal  beds.  Overlying  these  is  sandstone,  often  with  conglomerate 
layers.  If  the  mass  of  coaly  shale,  sandstone,  and  mostly  fine  conglom- 
erate so  far  described  be  conceded  to  re^^resent  the  basal  beds  of  the 
Carboniferous  series  in  this  region,  then  the  very  coarse  conglomerate  so 
abundantly  exposed  in  the  bed  of  the  farm  road  on  the  west  side  of  Wind- 
mill Hill  may  be  considered  as  representing  a  higher  horizon  and  as  over- 
lying at  least  the  great  mass  of  the  sandstones. 

If  this  view  be  correct,  the  coarse  conglomerate  on  the  west  side  of 
Windmill  Hill  could  then  be  correlated  with  the  coarse  conglomerates 
exposed  at  High  Hill  Point,  Fogland  Point,  the  northwest  side  of  Nonquit 
Pond,  and  thence  northward. 


278  GEOLOGY  OF  THE  NAREAGANSETT  BASIN. 

COARSE    COjSTGIjOMERATB   SERIES    ALOKG  THE  EAST  SHORE    OF 
SAKONNET   RIVER. 

HIGH    HILL    POINT. 

Southeast  of  High  Hill  Point,  near  the  western  end  of  the  beach,  is  an 
exposure  of  very  coarse  conglomerate,  with  pebbles  often  15  inches  long. 
An  included  sandstone  layer  shows  the  dip  to  be  about  10°  E.  At  the 
south  end  of  High  Hill  Point  the  coarse  congloiuerate  is  again  exposed. 
Near  the  east  there  is  an  included  sandstone  bed  showing  horizontal  bedding. 
Farther  west,  and  higher  up  the  cliff,  another  interbedded  sandstone  layer 
shows  a  dip  of  10°  W.  The  same  dip  is  shown  at  the  north  end  of  High 
Hill,  although  here  the  sandstone  layer  abuts  against  conglomerate  on  the 
east,  and  is  itself  cut  off  by  conglomerate  on  the  west,  so  abruptly  as  to 
make  the  real  bedding  at  first  sight  uncertain.  The  conglomerate  is 
exposed  in  a  small  indentation  north  of  the  hill,  and  continues  along  the 
bank  northward  for  a  short  distance.  Toward  the  west  of  the  most  northern 
exposure  of  the  coarse  conglomerate  a  fine  conglomerate  overlain  by  a  little 
sandstone  comes  in,  having  a  dip  of  30°  E.,  and  this  is  underlain  by  coarse 
sandstone,  which  in  certain  layers  is  so  full  of  very  small  pebbles,  an  inch 
and  less  in  size,  that  the  rock  may  be  termed  a  fine  conglomerate.  Occa- 
sionally the  rock  contains  coarser  layers,  with  pebbles  up  to  1  ^  or  2  inches 
in  length. 

The  great  mass  of  the  rock,  however,  is  sandstone  or  the  very  fine  con- 
glomerate. It  continues  to  be  exposed  northward  for  a  quarter  of  a  mile, 
the  dip,  however,  soon  diminishing  to  10°  E.  The  general  strike  of  the 
rocks  seems  to  be  about  N.  10°  E.  The  sandstone  is  very  similar  to  the 
sandstone  bordering  the  shore  southwest  of  Windmill  Hill,  southward 
toward  Browns  Point,  and  with  this  it  is  correlated.  The  overl}ang  coarse 
conglomerate  is  correlated  with  the  exposure  on  the  west  side  of  Windmill 
Hill,  just  west  of  the  farm  house. 

FOGLAND    POINT. 

A  short  distance  north  of  the  southern  end  of  the  headland  terminat- 
ing in  Fogland  Point,  the  very  coarse  conglomerate  with  large  pebbles  is 
exposed,  and  from  that  place  northward  it  borders  the  shore  halfway  to 
the  point.     The  strike  is  about  N.  10°  E.,  dip  10°  E.,  becoming  a  little  less 


WEST  OF  NONQUIT  POND.  279 

to  the  northward.  North  of  the  conglomerate,  ahnost  as  far  as  the  point, 
the  shore  hes  on  a  greenish  shale,  interbedded  with  a  schistose  rock  which 
is  evidently  a  sheared  sandstone  without  pebbles.  The  strike  of  this  rock 
is  about  N.  10°  to  20°  E.,  dip  10°  E.,  and  it  certainly  underlies  the  con- 
glomerate. Its  greenish  color  and  shaly  character  resemble  that  of  the 
rock  underlying  the  coarse  conglomerate  at  Eastons  Point.  At  the  southern 
end  of  the  headland  a  similar  greenish  shale  is  exposed,  also  striking 
N  10°  E.,  and  dipping  10°  E.  This  would  make  this  exposure  overlie  the 
coarse  conglomerate.  If  a  fault  be  supposed  to  intervene,  only  a  slight 
displacement  would  be  necessarj^  to  bring  up  the  lower  shales  to  this 
position.  This  green  shale  beneath  the  conglomerate  is  believed  to  be 
stratigraphically  related  to  the  sandstone  and  fine  conglomerate  series  below 
the  conglomerate  at  High  Hill  Point. 

EXPOSURES    WEST    OF    NONQUIT    POND. 

A  barrier  beach  connects  the  headland  of  Fogland  Point  with  the 
mainland.  East  of  the  beach  lies  a  broad  hill,  crossed  by  an  east- 
west  road.  On  the  western  side  of  the  hill  the  road  is  crossed  by  a  long 
set  of  very  coarse  conglomerate  exposures,  the  strike  of  an  interbedded 
sandstone  being  about  north-south.  This  exposure  lies  not  far  west  of 
the  line  of  strike  of  the  exposure  on  the  west  side  of  Windmill  Hill,  with 
which  these  various  conglomerates  are  correlated. 

A  quarter  of  a  mile  south  of  Coreys  Wharf  a  bluish-gray  to  black  shale 
or  fine-grained  sandstone  is  exposed,  some  of  the  layers  being  very  black 
and  shaly.  A  short  distance  south  of  Coreys  Wharf  the  rock  is  a  bluish 
sandstone.  No  trustworthy  strikes  and  dips  could  be  followed  for  any  dis- 
tance; but  these  exposixres  are  believed  to  underlie  the  coarse  conglomerate. 
Lithologically  they  are  somewhat  similar  to  the  more  northern  rocks 
exposed  along  the  shore  west  of  Windmill  Hill. 

The  very  coarse  conglomerate  is  exposed  at  various  points  alono-  the 
80-foot  hill  west  of  the  north  end  of  Nonquit  Pond.  North  of  the  east- 
west  road  one  interbedded  layer  of  sandstone  shows  a  westward  dip  of 
10°.     The  strike  is  probably  about  N.  10°  E. 


280  GEOLOGY  OF  THE  NAR  HAG  AN  SETT  BASIN. 

EXPOSURES  BETWEEN  TIVERTON   FOUR  CORNERS  AND  THE  NORTHEAST  SIDE 
OF    NANNAQUACKET    POND. 

Northwest  of  Tiverton  Four  Corners  a  tract  of  meadow  land  and  marsh 
runs  toward  the  bay  North  of  this,  a  Httle  east  of  north  from  the  last 
exposure  described,  the  coarse  conglomerate  is  exposed  in  several  places. 
The  more  northern  exposure  shows  a  strike  of  N.  32°  E.,  dip  50°  W. 
Eastward,  on  the  western  side  of  the  hill,  west  of  the  road,  are  several 
exposures  of  coarse  conglomerate  not  showing  a  marked  strike  or  dip. 
The  line  of  strike  of  the  exposure  described  above,  if  extended,  would  reach 
a  hill  showing  steep  cliffs  on  the  western  face,  where  interbedded  sandstones 
show  successively,  northward:  strike  N.  50°  W.,  dip  60°  W.;  strike  N.  75° 
W.,  dip  nearly  vertical,  and  strike  N.  30°  W.,  dip  70°  W.  Northward  a 
small  exposure  shows  a  strike  N.  5°  E.,  dip  about  70°  W.  A  large  steep  expo- 
sure northward  has  the  same  northerly  strike.  The  next  has  a  strike  N.  45° 
W.,  dip  60°  W.  Northeastward,  nearer  the  road,  are  several  exposures,  the 
most  western  of  which  has  a  strike  north-south,  dip  steep  west.  Then, 
after  a  rather  long  interval,  in  the  southeast  angle  of  the  crossing  of  the 
Tiverton  with  the  Sapowet  Point  road,  the  coarse  conglomerate  is  exposed 
again  with  a  strike  of  N.  70°  W.,  dip  35°  SW.  The  most  westerly  exposure 
north  of  the  Sapowet  Point  road  shows  a  strike  also  N.  65°  W.,  dip  60°  W. 
Nearer  the  crossroads  the  dip  seems  very  low  southwest.  At  an  inter- 
mediate point  northward  the  strike  is  N.  15°  W.,  dip  30°  W.  No  satis- 
factory bedding  is  shown  by  the  exposures  in  the  little  creek  which  runs 
west  about  a  quarter  of  a  mile  from  the  crossroads.  In  the  valley  of  this 
brook,  however,  a  little  east  of  the  line  of  outcrop  of  the  conglomerate,  occurs 
a  sandstone  and  shale  exposure,  in  places  of  a  rather  dark  color,  which 
may  represent  the  sandstone  series  underlying  the  coarse  conglomerate. 
Unfortunately,  the  exposure  is  not  large  enough  to  determine  the  matter. 

North  of  this  little  stream,  on  the  western  side  of  the  summit  of  the 
hill,  a  series  of  exposures  continues  northward.  One  of  these  shows  a 
strike  N.  40°  E.,  dip  steep,  perhaps  60°  W.  (uncertain).  The  most  northern 
exposure,  on  the  north  side  of  a  circular  embankment,  shows  strike  N.  80° 
E.,  dip  85°  N.  Northeast  of  the  private  road,  on  the  slope  toward  Naniia- 
quacket  Pond,  an  exposure  has  a  strike  N.  85°  E.,  dip  75°  N.  After  that 
the  exposures  continue  to  trend  northward  east  of  Nannaquacket  Pond. 
Coarse  conglomerate  is  exposed  along  the  Tiverton  road  not  far  north  of 


LITTLE  COMPTON  SHALES.  281 

the  southern  end  of  the  pond;  strike  N.  85°  W.,  dip  60°  S.  Northwest, 
near  the  end  of  a  point  projecting  into  Nannaquacket  Pond,  is  dark,  ahnost 
black,  sandstone,  which  seems  to  strike  N.  75°  W.,  dip  almost  vertical. 
It  may  be  sandstone  belonging  beneath  the  coarse  conglomerate  series.  In 
that  case  a  fault  or  sharp  anticlinal  fold  must  be  imagined  along  its  north- 
east side.  At  the  bend  of  the  road,  nearly  east,  the  conglomerate  strikes 
N.  75°  W.,  dip  70°  S.  Near  the  north  end  of  the  hill  forming  this  exposure 
unsatisfactory  exposures  indicate  a  strike  of  N.  35°  W.,  dip  70°  E.  North 
of  a  small  stream  a  small  hill  occurs  west  of  the  road.  Near  its  southern 
end  coarse  conglomerate  is  exposed.  Northwest,  at  the  shore,  an  inter- 
bedded  sandstone  layer  shows  strike  N.  3°  E.,  dip  apparently  50°  W. 
South  of  the  creek  and  east  of  the  road  numerous  bowlders  of  dark-blue 
to  black  sandstone,  sometimes  shaly,  occur  toward  the  northern  end  of  a 
hill.  The  trend  of  the  hill  is  N.  10°  E.  These  sandstones  are  of  the  kind 
which  underlie  the  coarse  conglomerate  series  and  which  are  found  eastward 
in  the  series  resting  upon  the  granite  associated  with  and  over  the  arkoses. 

The  greatly  varying  strike  and  dip  of  the  coarse  conglomerate  series 
here  described  may  be  partly  due  to  cross  bedding.  In  still  larger  meas- 
ure, however,  it  is  the  result  of  the  breaking  up  of  the  conglomerate  series 
by  a  system  of  faults  into  numerous  large  masses  or  blocks,  with  frequent 
and  variable  tilting,  but  not  enough  to  disguise  the  essential  unity  of  the 
series.  In  general  these  blocks  show  a  northward  strike  and  westward  dip. 
At  Fogland  and  High  Hill  Points,  however,  there  are  low  eastward  dips 
showing  a  shallow  syncline  between  this  and  Windmill  Hill.  Southward 
this  syncline  probably  became  strongly  accentuated,  giving  rise  to  the  steep 
eastward  dips  of  the  coarse  conglomerates  on  the  west  side  of  Sakonnet 
River  from  Black  Point  to  Smiths  Beach. 

On  the  west  side  of  the  neck  west  of  Nannaquacket  Pond,  about  two- 
thirds  of  its  length  from  its  north  end,  occur  several  exposures  of  grayish 
sandstone  and  of  conglomerate  with  medium-sized  pebbles,  of  which  the 
stratigraphic  position  can  not  be  determined. 

LITTLE   COMPTOK  SHALES. 

From  Browns  Point  to  the  south  side  of  Pachet  Brook  southward, 
within  half  a  mile  of  the  road  running  north  from  Little  Compton,  thence 
westward  and  along  the  shore  as  far  as  the  granite  area,  extends  a  series  of 
slates  and  shales  which  evidently  constitute  a  geological  unit.     The  most 


282  GEOLOGY  OF  THE  NAEEAGANSETT  BASIN. 

northern  exposure  of  these  shales  along  the  shore  is  at  Browns  Point,  along 
the  northerly  trend  of  the  shore  line.  A  second  similar  exposure  occurs 
where  the  shore  turns  toward  the  southeast.  The  strike  of  the  more 
northern  exposure  is  N.  32°  E.,  dip  45°  E.  The  more  southerly  exposure 
has  a  strike  N.  20°  E.,  dip  4.5°  E.  The  rock  is  of  a  greenish  color,  and 
has  been  cleaved  like  the  rocks  east  of  the  brook. 

The  next  exposure  of  the  series  occurs  almost  east  of  the  mouth  of  the 
brook,  a  little  south,  near  the  20-foot  level  on  the  hillside.  A  quarter  of  a 
mile  northward  exposures  occur  along  a  road  leading  eastward  up  the  hill. 
From  this  point  there  is  a  succession  of  exposm-es  extending  northeastward 
up  the  hillside.  This  line  of  outcrops  crosses  the  road  at  one  of  its  more 
marked  bends  on  the  summit,  continuing  in  the  northeasterly  direction 
alono-  the  hilltop  and  down  the  northeastern  slope  to  a  point  a  short  distance 
north  of  the  first  road  leading  east. 

The  series  evidently  underlies  the  whole  of  the  hill  east  of  Browns 
Point.  The  ordinary  appearance  of  the  rock  is  that  of  a  very  fine-grained 
whitish  quartzite  traversed  by  cleavage  planes,  usually  a  fifth  of  an  inch 
apart,  along  which  black  mica  is  abundantly  developed.  The  result  is  a 
general  stratified  appearance  of  the  rock,  the  strike  of  the  cleavage  being 
on  the  average  N.  40°  E.,  dip  very  steep,  almost  vertical.  Behind  the  barn, 
east  of  the  angle  of  the  road  mentioned  above,  the  rock  is  fine  grained, 
greenish,  slightly  banded  with  darker  material.  Southeast  of  this  hill  occurs 
another  elevation,  not  marked  upon  the  United  States  Geological  Survey 
map,  occupying  the  middle  area  of  the  quadrangle  formed  b}-  the  roads 
northwest  of  Little  Compton.  The  whole  of  this  hill  is  also  underlain  by 
the  cleaved  fine-grained  whitish  quartzitic  rock.  The  exposures  are  most 
frequent  on  the  western  and  southern  slopes.  The  more  northern  outcrops 
on  the  western  sides  show  a  cleavage  running  about  east- west;  farther  south 
and  southeast  it  runs  about  N.  25°  E.  The  rocks  are  here  evidently  much 
contorted  and  wrinkled.  The  stratification  in  places  is  clearly  not  in 
ao-reement  with  the  cleavage.  It  is  very  desirable  carefully  to  work  out 
the  real  plane  of  bedding  of  this  quartzitic  rock  and  to  determine  its  dip 
and  strike.  The  shore  exposures  farther  southwest,  however,  suggest  that 
the  general  dip  is  southeasterly. 

South  of  Browns  Point  is  a  cove.  At  the  headland  forming  its  south- 
ern extremity  the  rock  is  shaly.     Exposures  occur  southward  along  the 


BEOWNS  POmT  TO  CHUECHS  COVE.  283 

shore  at  low  tide.  A  third  of  a  mile  south  of  the  cove,  along  the  shore,  the 
fissile  green  shale  shows  purplish  coloring  along  certain  beds,  and  in  places 
there  seem  to  be  fine  bands  of  a  dolomitic  limestone  showing  a  pinkish 
coloring.  The  strike  here  is  N.  8°  E.,  dip  15°  E.  A  quarter  of  a  mile 
southward  the  sti-ike  is  N.  20°  E.,  dip  35°  E.  At  Churchs  Point  the  shales 
strike  N.  15°  E.,  dip  40°  E.  A  third  of  a  mile  southeast,  south  of  the 
mouth  of  a  small  stream,  there  is  an  exposure  too  massive  to  indicate  the 
attitude  of  the  beds.  Farther  south  close  observation  shows  a  fine-grained 
rock  cleaved  very  much  like  that  of  the  two  hills  toward  the  north,  first 
described;  strike  N.  30°  E.,  dip  40°  E.  Massive  rock  occurs  again  a 
quarter  of  a  mile  south  of  the  stream  last  mentioned,  in  a  small  indentation 
of  the  shore  line;  also  at  the  projecting  outline  farther  south,  and  at  the 
next  two  similar  projections  of  the  shore.  The  strike  is  apparently  N.  10° 
E.,  dip  60°  to  70°  E.  North  of  the  angle  in  Churchs  Cove  the  rock  has 
again  a  more  whitish  quartzitic  appearance;  strike  N.  10°  E.,  dip  25°  E. 
A  short  distance  south  of  the  point  where  the  shore  line  takes  a  southerly 
trend  the  greenish  shale  is  again  exposed.  Certain  layers  are  tinged  with 
purple,  and  pinkish  or  light-red  very  thin  dolomitic  bands  are  again  seen; 
strike  N.  15°  E.,  dip  15°  E.  The  greenish  shales  continue  to  be  exposed 
all  along  the  shore  as  far  as  the  granite  area.  Just  north  of  the  granite  area 
they  are  again  frequently  tinged  with  purple  and  also  show  the  very  thin 
dolomitic  bands.  Their  strike  is  N.  3°  E.,  dip  20°  E.  The  tingeing  of 
purple  with  the  thin  banding  of  dolomitic  material  suggests  that  these  shales 
are  identical  with  the  shales  forming  the  western  third  of  Newport  Neck. 

A  distance  of  about  50  feet  intervenes  between  the  above-described 
shales  and  the  next  exposure  of  rock.  This  is  a  rather  dark  rock,  con- 
taining abundant  brecciated  fragments  of  a  dark-greenish  stone,  and  appar- 
ently also  fragments  derived  from  a  granitic  mass.  It  strikes  in  a  direction 
about  N.  40°  E.,  and  evidently  follows  the  northern  line  of  the  granite  mass. 
It  is  believed  to  be  a  breccia  formed  during  the  faulting  which  brought  the 
shales  and  the  granite  into  juxtaposition  here. 

The  green  Little  Compton  shales  are  believed  to  be  of  pre-Carbonifer- 
.ous  age.  The  granites  on  the  south  are  also  considered  pre-Carboniferous. 
The  granites  may,  however,  be  more  recent  than  the  Little  Compton  shales. 
In  that  case  the  shales  near  the  contact  would  appear  more  massive  and 
more  like  hornstone,  resembling  the  Dumpling  rock  south  of  Jamestown  on 
Conanicut. 


CHAPTER   VI. 

AQUIDNECK,  OR  THE  ISLAND  OF  RHODE  ISLAND,  WITH  THE 
ISLANDS  OF  NEWPORT  HARBOR. 

ARKOSE  AND  PRE-CARBOIiriFEROUS  ROCKS  ON  8ACHUEST  NECK. 


At  the  promontory  almost  half  a  mile  south  of  Flint  Point,  greenish 
shaly  rocks  are  exposed  along  the  immediate  shore,  but  farther  out  the 
promontory  is  composed  of  arkose.  Interbedded  layers  of  coaly  shale  show 
that  the  arkose  occurs  in  the  form  of  a  low  anticline,  whose  axis  pitches 
northward  at  a  low  angle  and  trends  parallel  to  the  general  coast  line,  about 
N.  20°  E.  It  is  evidently  a  great  block  of  grit  which  once  lay  above  the 
level  of  the  green  shale  series,  but  was  dropped  by  faulting  down  to  its 
present  position  in  the  green  shale  area. 

Along  the  shore  the  green  shales  occur  as  far  northward  as  a  point  a 
quarter  of  a  mile  south  of  Flint  Point.  Here  they  change  from  their  former 
trend  of  N.  20°  E.,  dip  60°  W.,  to  N.  45°  E.,  dip  35°  W.  A  short  distance 
north  the  arkose  series  comes  in  with  a  similar  strike  and  a  nearly  vertical 
or  steep  western  dip.  The  strike  changes  rapidly  to  N.-S.,  dip  45°  to 
60°  W.,  and  continues  as  far  as  the  quartz-veined  promontory  southeast 
of  Flint  Point.  Between  this  and  Flint  Point  interbedded  coaly  shales 
show  that  the  arkose  series  dips  about  70°  W.  West  of  the  point  the  dip 
becomes  almost  vertical,  then  70°  to  60°  E.,  then  75°  E.,  60°  E.,  35°  E., 
and  80°  E.,  the  exposures  of  the  arkose  series  terminating  on  the  shore 
about  600  feet  southwest  of  the  point.  A  closer  examination  of  the  line 
of  exposure  between  this  more  western  point  and  Flint  Point  shows  that 
the  arkose  is  here  several  times  closely  folded,  the  western  sides  of  the 
folds  being  sometimes  a  little  overturned,  in  consequence  of  which  there 
appears  to  be  a  fairly  general  steep  eastward  dip.  Coaly  shale  layers 
are  frequently  interbedded  with  the  arkoses,  the  latter,  however,  predomi- 
nating.   These  coaly  shale  layers  are  very  numerous  elsewhere  in  the  series, 

284 


ARKOSE  ON  SAGHUEST  NECK.  285 

and  are  frequently  present  on  the  west  and  southeast  sides  of  Sachuest 
Neck.     On  these  sides  at  least  300  feet  of  arkose  matei'ial  is  exposed. 

On  the  western  side  of  Sachuest  Neck  the  exposures  begin  not  far  from, 
the  beach.  A  coaly  shale  bed  belonging  in  the  arkose  series  lines  the  shore 
at  its  upper  margin,  against  the  hillside,  for  a  long  distance.  Fern-leaf 
impressions  and  species  of  Annularia  occur  in  this  layer  just  northwest 
of  some  old  farm  buildings.  The  dip  is  about  vertical  or  at  times  very- 
steep  eastward  at  the  north  end,  but  southward  it  is  more  regularly  and 
decidedly  west.  Westward,  near  low-tide  levels,  the  arkoses  show  a  lower 
western  dip,  and  this  low  westward  dip  becomes  more  marked  and  more 
general  southward.  At  very  low  tide  the  arkose  series  is  seen  to  change 
from  its  ordinary  strike  of  N.  15°  E.  to  N.-S.,  and  then  to  N.  20°  W.  north- 
ward at  one  point  near  the  northern  end  of  these  western  exposures.  These 
features  probably  indicate  a  secondary  synclinal  structure  west  of  the  neck. 
The  westward  dips  continue  as  far  as  the  point.  Near  the  point  the  strike 
is  about  N.  23°  E.,  dip  45°  W.  Along  the  east  side  of  the  point  there  is  a 
well-marked  fold  whose  axis  trends  N.  8°  E.  This  can  be  followed  north- 
eastward along  the  shore,  and  250  feet  north  from  its  most  southern  expo- 
sure the  axis  of  the  fold  turns  quite  abruptly  eastward,  so  as  to  trend 
N.  50°  E.  Then  it  changes  again  to  a  more  northerly  direction,  showing 
synclinal  structure  on  the  northwest  side,  and  on  a  larger  scale  on  the 
southeast,  the  trend  northward  seeming  to  be  N.  16°  E.  Not  far  from  the 
most  northeastern  exposures  of  the  arkose  series  a  small  fold  is  shown,  its 
axis  trending  N.  8°  E.,  its  anticlinal  nature  being  not  &,t  first  sight  very 
noticeable,  owing  to  a  slight  overturn  of  the  fold  in  part  of  the  exposure. 
The  most  eastern  arkose  exposures  show  a  strike  about  north-south ;  the  dip 
is  about  20°  to  30°  W.  Along  this  most  eastern  exposure  the  arkose  at 
low  water  shows  on  the  east  of  the  normal  arkose  a  very  granitic-looking 
rock  in  which  the  feldspar  can  be  easily  recognized.  Farther  up  the  beach, 
near  high-water  mark,  the  arkose  shows  at  its  base  a  mass  of  unquestioned 
coarse  porphyritic  granite,  about  3  feet  long,  with  phenocrysts  of  feldspar, 
like  those  at  the  Cormorant  Rock,  over  a  mile  southward,  and  elsewhere. 
It  can  not  be  determined  whether  this  is  only  an  included  bowlder  or  the 
upper  part  of  the  granitic  mass  which  once  furnished  the  material  for  the 
arkose.  From  the  well-preserved  feldspars  in  the  granitic  rock  toward 
the  sea,  it  is  evident  that  if  this  lower  rock  be  not  itself  g-ranite  the  original 


286  GEOLOGY  OF  THE  NAERAGANSETT  BASIN. 

granite  mass  could  not  have  been  far  away.  It  seems  probably  that  the 
porph3a'itic  granite  near  high-tide  level  niay  be  a  part  of  the  original 
granite  mass  and  not  a  bowlder  derived  from  the  same.  The  existence  of 
this  granite  with  large  feldspar  phenociysts  at  Little  Compton,  and  south- 
east of  Almys  Pond,  south  of  Newport,  as  well  as  at  the  Cormorant  Rock, 
makes  such  a  supposition  not  impossible. 

PRE-CARBONIFEROUS    ROCKS. 

The  Island  Rocks  and  other  associated  rocks  off  the  northeast  coast  of 
Sachuest  Neck  are  all  composed  of  a  greenish  rock,  varying  between  a 
slate  and  a  shale,  striking  about  N.  24°  E.  and  dipping  westward.  The 
Island  Rocks  resemble  very  much  the  more  quartzitic  rock  in  the  hill 
exposures  east  of  Browns  Point.  The  green  shales  are  also  exposed  along 
the  east  shore  of  Sachuest  Neck,  from  a  point  a  quai'ter  of  a  mile  south  ot 
Flint  Point  to  the  arkose  promontory  a  quarter  of  a  mile  farther  south. 
Near  its  northern  end  the  shale  contains  a  little  conglomerate,  striking  N. 
43°  E.,  dip  35°  W.  This  changes  soon  to  strike  N.  33°  E.,  dip  60°  W., 
this  strike  and  dip  being'  maintained  as  far  as  the  arkose  promontory.  At 
the  north  end  of  the  cove,  southwest  of  the  promontory,  the  rocks  strike 
N.  35°  E.,  dip  35°  W. ;  southward  in  the  cove  the  strike  changes  to  N.  40° 
E.,  then  N.  45°  E.  toward  the  southern  side  of  the  cove,  changing  to  N. 
30°  E.,  dip  60°  W.,  near  the  south  end  of  the  cove.  The  more  southern 
exposures  along  the  cove  show  considerable  conglomerate  with  angular 
fragments,  and  from  this  point  southward  most  of  the  rock  is  conglomeratic- 
A  whitish  sandy  band  makes  its  appearance  in  the  cong-lomeratic  greenish 
rock.  It  is  similar  to  some  of  the  more  quartzitic  rock  in  the  Little  Comp- 
ton shale  series  on  the  hill  east  of  Browns  Point.  This  can  be  followed  for 
a  considerable  distance,  having  strike  N.  30°  E.,  dip  60°  W.  at  the  north 
end,  becoming  steeper  southward.  The  shore  here  makes  a  convex  curve. 
Toward  the  southern  end  of  this  the  strike  is  still  N.  33°  E,,  dip  80°  W., 
but  immediatelv  beyond  the  strike  becomes  N.  58°  E.,  dip  70°  E.,  chang- 
ing soiithward  to  N.  53°  E.,  dip  60°  E.,  and  then,  at  another  convex  curve 
in  the  shore  line,  to  N.  35°  E.,  dip  45°  E.  Southward  there  is  a  small 
promontory  halfway  between  the  arkose  promontory  and  Sachuest  Point 
The  strike  here  is  N.  63°  E.,  dip  60°  E.  West  of  the  cove  formed  by  this 
promontory  the  strike  is  N.  22°  E.,  dip  80°  E.,  becoming  N.  30°  E.,  dip 


PEE  CARBONIFEROUS  ROCKS  OF  SACHUEST  NECK.     287 

80°  E.,  at  the  line  of  faulting-  separating  this  rock  from  the  arkose  series.^ 
A  short  distance  east  of  this  fault  line  the  rock  contains  a  diabase  dike. 

It  will  be  noticed  that  about  halfway  between  the  southern  termina- 
tion of  the  greenish  conglomeratic  rock  and  the  arkose  promontory  the  dip 
changes  from  steep  east  to  steep  west.  North  of  the  point  the  exposures 
seem  to  be  successively  lower.  Southward  toward  the  fault  line  appai-- 
ently  higher  horizons  are  reached.  Close  observation,  however,  shows  no 
signs  of  a  fold  there,  where  the  steep  dips  change  du-ection.  A  strong 
flexure  in  the  rock  previous  to  the  faulting  which  exists  farther  westward 
seems  to  be  the  explanation,  the  flexure  being  of  such  a  character  that  at  a 
certain  point  the  conglomeratic  strata  are  nearly  vertical.  North  of  this 
point  they  dip  westward;   south  of  this  point,  eastward. 

Exposures  of  the  greenish  congdomerate  also  occur  on  the  hillside 
toward  the  southern  part  of  the  hne  of  shore  exposures.  A  line  connect- 
ing the  extreme  shore  exposures  west  and  south  would  trend  N.  22°  E., 
and  would  pass  just  west  of  the  most  western  of  the  hill  exposures. 

The  position  of  the  conglomerate  with  reference  to  the  greenish  shales 
is  luicertain,  but  after  detailed  work  on  this  question  it  was  supposed  to 
overlie  the  same,  owing  to  the  westward  dip  of  the  series  northward 
toward  the  Island  Rocks. 

While  the  shales  have  the  ordinary  clastic  appearance  the  conglomeratic 
beds  present  certain  peculiar  features.  In  the  first  place,  the  pebbles  are 
usually  decidedly  angular  in  appearance,  presenting,  commonly,  the  aspect 
of  fragments  in  a  breccia.  In  the  second  place,  there  seems  to  be  no  marked 
tendency  to  arrange  the  fragments  in  layers  according  to  size,  as  is  commonly 
the  case  when  fragments  are  transported  by  water  action.  In  the  third  place, 
a  lai'ge  part  of  the  fragmental  material  is  lighter  or  darker  in  color  than  the 
cementing  material  when  seen  on  the  weathered  surface  of  the  rock.  When 
broken,  however,  this  distinctness  to  a  great  extent  disappears,  and  the  whole 
mass  looks  greenish,  varying  chiefly  in  fineness  of  grain.  This  is  a  feature 
more  commonly  observed  in  breccias  than  in  genuine  conglomerates.  In 
the  fourth  place,  the  variety  of  material  occurring  in  the  form  of  fragments 
varies  sufficiently  to  include  four  or  five  types.  Some  of  these  fragments 
seem  to  be  certainly  from  some  clastic  rock.     Others  ms,j  be  of  igneous 

'  Prof.  T.  Nelson  Dale  raises  the  very  pertinent  question  wliether  the  facts  may  not  be  explained 
by  assuming  an  unconformity,  since  Carboniferous  arkose  would  probably  rest  in  an  unconformable 
manner  upon  Cambrian  shale. 


288  GEOLOG^Y  OF  THE  NAERAGANSETT  BASIN. 

origin,  but  they  do  not  resemble  any  known  rock  in  the  Carboniferous  basin. 
Fragments  of  a  reddish  rock,  often  resembhng  jasper,  occur  here  and  there. 
In  the  fifth  place,  the  absence  of  granite  in  the  form  of  pebbles  is  very 
noticeable. 

In  several  of  these  particulars  the  greenish  Sachuest  conglomeratic  rock 
resembles  the  more  northern  exposures  of  the  Dumpling  rock  on  the  eastern 
shore  of  Conanicut,  south  of  Jamestown.  There  seems  to  be  no  question 
of  the  pre-Carboniferous  character  of  the  greeriish  rock,  both  shale  and 
conglomerate.  The  absence  of  all  granite  fragments  from  the  green  series 
suggests  that  the  granite  is  intrusive  and  therefore  of  later  origin.  The 
nearest  granite  exposures  of  any  size  are  now  at  Cormorant  Rock,  but  the 
ex^Dosure  just  beneath  the  arkose  series  suggests  that  it  once  reached  as  far  as 
Sachuest  Neck.  The  arkose  series  probably  once  rested  upon  the  green 
series,  a  relation  now  obscured  by  faulting.  It  derived  its  materials,  at  least 
the  coarser  part,  from  the  granite,  which  is  therefore  pre-Carboniferous.  The 
grit  is  Carboniferous,  as  is  shown  by  the  interbedded  coaly  shale  layers 
containing  fossils.  The  interbedding  of  coaly  fossiliferous  shales  with  the 
grit  seems  to  be  characteristic  of  exposures  along  the  eastern  margin  of  the 
Narragansett  Basin,  several  such  occurrences  being  known  at  Steep  Brook, 
Fall  River,  and  Tiverton.  The  relative  age  of  this  eastern  arkose  as  com- 
pared with  that  of  the  Aquidneck  shale  series  can  not  be  determined  at 
present. 

EASTERN   SHORE   OF  AQUIDTSTECK   ISLAND  AS   FAR   SOUTH  AS   THE 
SECOND  COV3  NORTHWEST  OF  BLACK  POINT. 

The  most  northern  exposure  of  Carboniferous  rock  on  Aquidneck 
Island  on  the  east  shore  occurs  southwest  of  the  cove,  near  the  eastern 
base  of  Butts  Hill.  Coaly  shale  and  sandstone  are  interbedded,  being 
several  times  repeated  southward  for  half  a  mile,  as  far  as  the  wharf  east 
of  Portsmouth  village.  North  of  the  wharf  a  short  distance  there  is  evidence 
of  a  low  anticline,  pitching  southward,  the  dip  being  low  on  both  sides. 
The  exposures  at  the  wharf  and  southward  belong  to  the  western  side  of 
this  anticline,  and  therefore  all  dip  westward.  At  the  wharf  there  is  sand- 
stone on  the  north  side,  showing  a  cleavage  dipping  60°  W.  Overlying 
the  sandstone  on  the  south  side  is  a  thin  \fijer  of  conglomerate  dipping 
about  10°  E.  But  south  along  the  shore  exposures  of  conglomerate 
and  dark  coaly  shales  strike  N.  3°  E.,  dip  45°  W.     Southward  sandstone 


EASTERN  SHORE  OF  AQUIDNECK  ISi^AJSTD.  289 

borders  the  shore,  interbedded  with  a  few  coaly  shale  layers  and  a  few 
thin  conglomerate  beds  with  small  pebbles  and  flakes  of  carbonaceous 
shale;  strike  N.-S.,  dip  20°  W.  Yet  farther  south  gray  sandstone  is 
abundant.  Interbedded  with  this,  south  of  a  small  stream,  a  third  of  a 
mile  from  the  wharf,  is  black  coaly  shale;  strike  N.-S.,  dip  30°  W. 

Half  a  mile  south  of  the  wharf  the  coaly  shale  contains  impressions 
of  fern  leaves;  strike  N.  3°  E.,  dip  40°  W.  Southward  occurs  sandstone, 
overlain  by  several  feet  of  fine  conglomerate,  the  pebbles  not  exceeding 
1  inch  in  length;  dip  30°  W.  PYom  the  wharf  southward  rocks  con- 
tinually higher  in  the  series  are  exposed,  but  owing  to  the  fact  that  the 
strike  is  almost  parallel  to  the  shore,  only  a  small  thickness  of  strata  is 
traversed. 

From  this  fine  conglomerate  exposure  southward  the  strike  seems  to 
be  a  little  east  of  south,  while  the  shore  line  curves  inward  in  such  a  way 
as  to  expose,  a,  third  of  a  mile  southward,  gray  sandstone  in  the  form  of 
large  loose  blocks.  Then,  two-fifths  of  a  mile  southward,  large  blocks  of 
coaly  shale  occur,  representing  the  highest  rocks  so  far  described.  A  third 
of  a  mile  southward  the  gray  sandstone  seems  to  be  repeated,  descending 
in  the  series;  strike  N.  7°  W.,  dip  10°  W. ;  and  only  a  short  distance 
beyond,  southward,  the  almost  horizontal  sandstone  contains  thin  con- 
glomerate layers  with  pebbles  up  to  1  inch  in  length.  The  more  southerly 
of  these  exposures  dip  10°  W.  The  thin  conglomerate  layers  continue  to 
occur  in  the  sandstone  southward,  and  at  several  places  they  contain  the 
fragments  or  flakes  of  coaly  shales  noted  above. 

In  the  Glen  almost  half  a  mile  of  exposure  is  seen.  The  rock  is 
evidently  the  shale  series,  very  much  blacker  and  more  coaly  than  the 
corresponding  rocks  on  the  west  side  of  the  island.  East,  toward  the  bay, 
about  25  feet  above  the  water  level,  a  Cordaites  leaf  was  found  in  the 
shale.  About  40  feet  above  the  water  level  there  is  sandstone  interbedded. 
A  comparison  of  the  Glen  section  with  the  shore  exposures  from  McCurrys 
Point  southward  beyond  Sandy  Point  shows  that  the  shore  exposures  also 
belong  to  the  shale  series.  As  far  as  can  be  determined  the  shale  series  at 
the  Glen  di^DS  low,  5°  or  10°  E.     It  certainly  is  nearly  horizontal 

Between  the  Glen  and  the  beach  of  Sandy  Point  there  is  exposed 
sandstone  sheared  into  a  shaly  rock,  the  shearing  planes  dipping  east  of 
south.     No  bedding  could  be  recognized.     South  of  the  beach  of  Sandy 

MON  XXXIII 19 


290  GEOLOGY  OF  THE  NARRAGANSETT  BASIN. 

Point  coaly  shale  comes  in  again.     A  quarter  of  a  mile  soiithward  this  has 
evidently  been  violently  squeezed  in  an  east-west  direction. 

South  of  McCurrys  Point  a  small  stream  entering  the  bay  from  the 
west  exposes  from  the  shore  to  a  considerable  distance  up  the  hill  westward 
nothing  but  bluish-black  shale  of  the  type  found  so  abundant  on  the  west- 
ern side  of  the  island  over  the  coal  regions.  These  bluish-black  shales 
evidently  overlie  the  coaly  shales,  sandstones,  and  fine  conglomerates  so 
far  described,  and  a  small  fault  has  probably  thrown  them  a  little  eastward 
near  the  point.  The  cleavage  obscures  the  stratification.  The  cleavage 
dips  15°  to  20°  W.,  and  there  seems  to  be  a  southward  dip  of  perhaps  no 
more  than  5°.  Southward  the  shale  becomes  blacker  and  more  coaly  and 
seems  to  be  nearly  horizontal.  A  quarter  of  a  mile  north  of  the  mouth  of 
the  creek  traversing  the  Glen  it  contains  impressions  of  fern  leaves.  The 
coaly  shale  continues  as  far  as  the  Glen. 

A  mile  south  of  Sandy  Point,  or  a  little  over  half  a  mile  from  the 
southern  extremity  of  the  beach,  dark-gray  sandstone  makes  its  appearance 
again.  Over  it  occurs,  southward,  coaly  shale,  apparently  dipping  eastward, 
but  this  dip  is  of  little  moment,  since  southward  there  is  abundant  evidence 
of  violent  crumpling  and  folding  of  the  rock  by  a  force  acting  in  an  east- 
west  direction.     Southward  more  sandstone  is  seen  sheared  into  a  shale. 

The  absence  of  clear  indications  of  the  bedding  at  this  locality  and  as 
far  northward  as  McCurrys  Point,  and  the  violent  crumpling  at  the  last- 
described  locality  as  well  as  south  of  Sandy  Point,  afi"ord  serious  difficulties 
in  attempting  to  determine  the  stratigraphic  position  of  the  coarse  conglom- 
erates in  the  southeastern  part  of  Aquidneck. 

The  great  Aquidneck  shale  series  exposed  at  the  Glen  and  along  the 
shore  is  believed,  however,  to  be  overlain  north  of  Black  Point  by  the 
coaly  Sakonnet  sandstone  with  fine  conglomerate,  representing  a  section  of 
much  smaller  thickness,  110  feet  being  exposed  at  the  point,  and  this  in 
turn  is  overlain  by  the  coarse  Purgatory  conglomerate,  whose  maximum 
thickness  as  exposed  along  the  shore  apparently  does  not  exceed  380  feet. 

COARSE    CONGLOMERATES    AND    UNDERLYING    SANDSTONE    SERIES 
FROM  BLACK  POINT  TO  THE  NORTH  END  OF  SMITHS  BEACH. 

About  a  quarter  of  a  mile  northwest  of  Black  Point  is  a  second  promon- 
tory.    In  a  cove  immediately  toward  the  west  of  the  latter  is  bhiish  sand- 


BLACK  POINT  TO  TAGGARTS  FERRY.  291 

stone.  A  thin  conglomerate  layer  with  small  pebbles  shows  a  strike  of 
N.  53°  E.,  dip  at  first  lower,  then  30°  SE.  Eastward  along  the  strike 
the  sandstone  becomes  decidedly  darker  and  more  carbonaceous,  the  strike 
changing  to  N.  35°  E.  On  the  east  side  of  the  promontory  the  strike  is 
N.  32°  E.,  dip  45°  SE.  The  dark  carbonaceous  sandstone  series  is  con- 
tinued on  the  east  side  of  the  promontory  along  the  northern  side  of  the 
cove  north  of  Black  Point.  About  110  feet  of  the  sandstone  series  are 
exposed.  The  lower  90  feet  consist  of  the  carbonaceous  sandstones  already 
described,  with  which  are  intercalated  thin  conglomerate  beds  with  pebbles 
not  exceeding  1  inch  in  size.  Then  occurs  a  layer  of  coaly  shale  1  foot 
thick,  above  which  are  7  feet  more  of  the  dark  sandstone.  Above  are  8  feet 
of  conglomerate  with  small  pebbles,  and,  finally,  4  feet  of  the  dark  sand- 
stone. On  the  north  side  of  the  cove  north  of  Black  Point  the  strike  is 
N.  68°  E.,  dip  about  45°  SE.  Southward  there  is  no  exposure  until  the 
middle  of  the  cove  is  reached,  when  the  very  coarse  conglomerate  comes 
to  view. 

The  general  strike  of  this  conglomerate  is  about  N.  22°  E.  At  the 
northern  end  of  the  shore  exposures,  however,  there  is  marked  variation  in 
strike.  Near  the  middle  of  the  cove  the  conglomerate  includes  a  sandstone 
layer  apparently  striking  N.  3°  E.,  dip  80°  E.  Nearer  the  south  end  of  the 
cove  the  strike  is  N.  48°  E.,  dip  about  60°  E.  South  of  Black  Point  the 
strike  is  N.  28°  E.,  dip  60°  E.,  the  strike  becoming  about  N.  22°  E.  farther 
south. 

Notwithstanding  this  irregularity  in  the  strike  of  the  sandstone  and 
conglomerate  series,  and  especially  the  discordance  between  the  average 
strike  of  the  two  series,  the  sandstone  is  believed  to  underlie  the  coarse 
conglomerate,  the  dips  certainly  favoring  this  view. 

That  part  of  the  exposure  from  Black  Point  two-thirds  of  a  mile 
southward  is  serviceable  in  estimating  the  thickness  of  the  conglomerate 
series.  About  380  feet  of  the  coarse  conglomerate  series  are  exposed.  The 
lowest  part  of  the  section  is  found  near  the  northern  end  of  the  line  of 
exposures.  The  upper  beds  are  exposed  along  the  shore,  farther  south. 
Beginning  with  the  lowest  part  of  the  section,  four  beds  of  conglomerate 
maybe  distinguished,  19,  20,  11,  and  32  feet  thick.  Above  these  He  35 
feet  of  sandstone,  separated  by  a  thin  conglomerate  layer  from  29  feet  more 
of  sandstone;  next,  a  thin  black  shale  layer,  then  23  feet  of  conglomerate, 


292  GEOLOGY  OF  THE  NAREAGANSETT  BASIN. 

at  the  top  including  fragments  of  coaly  shale,  followed  by  a  4-foot  layer  of 
conglomerate,  also  including  fragments  of  coaly  shale  at  the  top.  Above 
the  conglomerate  are  2  feet  of  coaly  shale,  12  feet  of  conglomerate,  6  feet 
of  coaly  sandstone,  15  feet  of  grayish-black  sandstone,  5  feet  of  grayish 
sandstone,  2  feet  of  black  coaly  shale,  14  feet  of  dark-gray  sandstone,  two 
layers  of  conglomerate  15  and  7  feet  thick,  13  feet  of  sandstone,  and,  at  the 
top  of  the  section,  three  layers  of  conglomerate,  33,  23,  and  27  feet  thick. 

A  generalized  statement  of  the  chief  characteristics  of  this  section  would 
be  82  feet  of  coarse  conglomerate  at  the  base,  followed  by  99  feet  of  sand- 
stone, 41  feet  of  coarse  conglomerate,  42  feet  of  sandstone,  and  118  feet  of 
conglomerate.  The  thickness  of  the  great  interbedded  sandstone  layers 
should  be  especially  emphasized  when  the  attempt  is  made  to  determine 
the  relative  horizon  of  isolated  small  sandstone  and  coarse  conglomerate 
outcrops. 

Along  the  line  of  outcrop  described  above,  the  dip  varies,  southward, 
from  60°  E.  to  45°  and  40°  E.,  becoming  again  60°  E.  toward  the  southern 
end  of  the  section  described.  Southward  along  the  shore,  at  a  promontory 
a  mile  south  of  Black  Point,  the  dip  increases  to  80°  E.  The  steep  east- 
ward dip  continues  southward,  becoming  80°  W.  at  Taggarts  Ferry  Cove, 
bnt  returning  to  75°  E.  again  on  the  south  side  of  the  cove. 

The  very  coarse  conglomerate  borders  the  eastern  shore  of  Aquidneck 
Island  as  far  southward  as  the  north  end  of  Smiths  Beach,  except  in  tlie 
cove  two-fifths  of  a  mile  north  of  Woods  Castle,  known  as  Taggarts  Fen-}-, 
where  rocks  occur  varying  between  coaly  sandstone  and  coaly  shale. 

On  the  shore  west  of  the  southern  end  of  the  cove,  and  along  the 
creek  south  of  these  exposures,  dark  carbonaceous  shale  and  sandstone  are 
exposed  for  30  or  40  feet.  The  shale  series  is  believed  to  merge  gradually 
upward  into  this  peculiar  coaly,  carbonaceous  shale  and  sandstone.  East- 
ward along  the  shore  overlying  these  land  exposures  is  more  sandy  rock  of 
the  same  character.  Overlying  this  is  found  a  coarser  sandstone,  overlain 
in  turn  by  carbonaceous  shaly  rock,  the  dip  varying  from  vertical  to  85° 
W.  Then  comes,  eastward,  a  coarser  sandstone,  with  small  pebbles,  dipping 
80°  W.  Toward  the  north,  along  the  shore,  a  sudden  twist  causes  the  con- 
tact between  this  rock  and  the  overlying  carbonaceous  shale  to  dip  due 
east.     Farther  east,  coarser  sandstone,  with  fine  conglomerate  overlying  it, 


TAGGARTS  FEERY  TO  SMITHS  COVE.  293 

dips  more  steeply,  55°  E  Overlying  this,  conglomerate  with  medium- 
sized  pebbles  dips  70°  to  80°  E.  Then  comes  a  comparatively  thin  layer 
of  coaly  sandstone  and  a  conglomerate  with  pebbles  of  medium  size,  both 
dipping  80°  E.  Then  a  considerable  thickness  of  dark-gray,  more  car- 
bonaceous shaly  rock  is  exposed,  and  an  equall}^  thick  bed,  perhaps  40 
feet,  of  rather  coarse  conglomerate,  dipping  80°  E.  Overlying  this  occurs 
carbonaceous  sandstone,  with  coarse  conglomerate  farther  east;  dip  vertical 
or  80°  E.  along  the  promontory  which  they  form  at  the  north  end  of  the 
cove;  but  farther  north,  along  the  shore,  the  same  beds  dip  80°  W.  This 
same  dip,  varying  to  vertical,  is  shown  for  some  distance  northward,  until 
the  beds  gradually  incline  more  and  more  eastward,  as  already  noted. 
South  of  the  cove  the  dip  is  75°  E.  It  is  evident  that  the  same  beds  of 
coarse  conglomerate,  with  the  underlying  sandstone  series,  have  been 
folded  in  such  a  way  as  to  dip  more  steeply  in  coming  southward  along  the 
strike  toward  Taggarts  Ferry;  at  the  ferry  there  is  a  slight  overturn,  the 
dip  being  80°  to  70°  W.,  and  immediately  south  of  the  ferry  the  dip  returns 
to  75°  E.  with  sufficient  suddenness  to  denote  a  stronger  flexure  at  the 
southern  end  of  the  cove 

The  Sakonnet  sandstones  in  the  cove  and  westward  correspond  strati- 
graphically  to  the  sandstone  north  of  Black  Point. 

From  the  cove  southward  to  Woods  Castle  we  pass  from  lower  to 
higher  rocks  in  the  conglomerate  series.  The  dip  is  steeply  eastward — 
usually  about  70°  E.  At  Woods  Castle  a  bed  of  coaly  shale  occurs,  over- 
lying that  part  of  the  conglomerate  series  forming  the  shore.  It  contains 
abundant  fern  remains.  Eastward,  after  an  interval  of  perhaps  30  feet, 
probably  also  underlain  by  shaly  rock,  the  great  isolated  mass  forming  the 
conspicuous  feature  of  this  coast  line  is  exposed.  It  is  composed,  at  least 
on  the  west  side,  chiefly  of  coarse  sandstone.  The  stratigraphy  was  not 
carefully  followed,  but  the  coaly  shale  bed  seems  to  correspond  to  a  more 
sandy,  coaly  shale  exposed  about  a  quarter  of  a  mile  north  of  the  cove  at 
Taggarts  Ferry,  and  the  sandstone  overlying  it  replaces  a  coarse  conglom- 
erate. In  other  words,  the  fern  locality  at  Woods  Castle  occurs  well  within 
the  coarse  conglomerate  series,  and  not  overlying  the  same.  Southward, 
toward  Smiths  Cove,  the  dip  is  less  steep,  becoming,  near  the  southern  end, 
as  low  as  50°  or  even  45°  E. 


294  GEOLOGY  OF  THE  NAKKAGANSETT  BASIN. 

COARSE    COIVGLOMERATES    AND    UNDERLYING    ROCKS   ON  THE  NECK 
AT  EASTONS    POINT. 

Ou  the  eastern  side  of  the  neck,  at  the  west  end  of  Sachuest  Beach, 
the  very  coarse  conglomerate  series  is  well  exposed  along  the  shore  for  a 
length  of  almost  half  a  mile,  terminating  southward  in  a  long  narrow 
promontory  projecting  into  the  sea.  The  strike  of  this  conglomerate  is 
about  N.  20°  E.,  dip  60°  E.,  southward  becoming  only  45°  E.  "West- 
ward, beneath  the  conglomerate  is  greenish  sandstone,  often  shaly.  Inter- 
bedded  with  this  is  conglomerate,  but  not  equaling  the  sandstone  in 
quantity,  and  the  pebbles  are  also  much  smaller  than  those  in  the  very 
coarse  conglomerate.  The  dip  is  still  45°  E.  Southwestward  along  the 
shore,  still  lower  rocks  are  exposed — greenish  shaly  sandstone  and  shale, 
with  conglomerate  of  rather  small  pebbles.  The  dip  is  45°  E.,  and  the 
strike  is  still  N.  20°  E.  Thence  to  Eastons  Point  there  is  a  series  of 
underlying  greenish  shaly  sandstone  and  fissile  shales,  having  an  eastward 
dip.  So  far  the  exposures  beneath  the  coarse  conglomerate  are  so  little 
divergent  from  the  strike  of  the  shore  line  that  the  section  as  far  as  the 
point  does  not  represent  any  great  thickness.  Going  northwestward  from 
the  point,  we  meet  still  lower  rocks.  At  first  greenish  shaly  rock  continues 
the  descending  section,  containing  a  little  conglomerate  a  short  distance 
west  of  the  point.  At  one  point  west  of  the  southern  end  of  the  neck  ripple 
marks  are  seen  in  the  shales.  Nine  hundred  feet  northwest  from  the  point 
intercalated  sandstones  indicate  a  local  increase  of  dip  to  70°  E.,  and  then 
toward  the  axis  the  dip  is  lower  eastward.  The  axis  of  the  anticlinal  fold 
is  about  a  third  of  a  mile  northwest  of  Eastons  Point.  The  dip  on  both 
sides  is  low.     The  pitch  of  the  fold  is  about  10°  S. 

West  of  the  anticline  the  dip  is  at  first  low  W,  20°.  This  continues 
for  some  time  until,  about  half  a  mile  from  the  point,  the  dip  increases  to 
45°  W.,  the  strike  being  still  N.  13°  E.  Here  are  intei'calated  gray  sandstone 
and  conglomerate  composed  of  small  pebbles  corresponding  to  the  con- 
glomerate just  west  of  Eastons  Point.  Farther  northwest  the  conglomerate 
layers  become  I'ather  frequent,  the  dip  being  45°  W.;  and  this  continues  for 
some  distance  along  the  shore.  The  pebbles  are  only  of  medium  size. 
Locally  the  dip  becomes  steeper  west,  at  one  point  80°  W.,  but  it  soon  returns 
to  very  low  west,  and  then  45°  W.  again;  near  this  point  the  very  coarse 
conglomerate  makes  its  appearance  once  more,  about  three-fifths  of  a  mile 


PARADISE  ROCKS.  295 

from  Eastons  Point,  and  a  fifth  of  a  mile  southeast  of  the  first  exposures 
east  of  Eastons  Beach.  Northwestwai-d  the  coarse  conglomerate  continues, 
with  interbedded  sandstone  and  a  little  carbonaceous  shale.  The  dip 
decreases  from  45°  W.  to  15°  W.  Westward  along  the  shore  the  very 
coarse  conglomerate  with  interbedded  sandstone  continues,  the  most 
western  exposui-es  becoming  nearly  horizontal,  dipping  at  a  low  angle  east- 
ward, from  5°  to  10°  perhaps.  At  the  extreme  western  end  of  the  exposures 
the  conglomerate  shows  an  interbedded  layer  of  dark  carbonaceous  sand- 
stone, so  disjointed  by  small  faults  along  joints  as  to  obscure  at  first  sight 
the  evidences  of  its  former  continuity.  This  layer,  when  reconstructed, 
indicates  an  eastward  dip  of  10°  to  15°. 

Comparing  the  two  sides  of  the  anticlinal  fold,-  the  western  side  is  seen 
to  have  a  lower  dip.  This  feature  is  especially  well  shown  near  the  extreme 
ends  of  the  shore  exposures,  the  dip  at  the  Purgatory  rocks  being  at  least 
60°  E.,  while  on  the  west  side  the  dips  for  a  long  distance  along  the  shore 
are  low  west,  and  then  east,  being  in  places  practically  horizontal.  The 
shales  on  the  western  side  of  the  fold  are  perhaps  a  little  more  carbonaceous, 
but  in  general  the  rocks  show  only  a  dark-gray  color.  In  comparison  with 
this  the  shale  and  sandstone  series  at  Taggarts  Ferry  are  very  much  darker, 
often  black,  and  show  a  similar  intercalation  of  medium-sized  conglomer- 
erates  just  below  the  coarse  conglomerate  series.  Near  Black  Point  the 
series  contains  chiefly  sandstone,  which,  although  carbonaceous,  is  not  so 
dark  as  the  Taggarts  Ferry  exposure.  Moreover,  the  change  from  fine 
conglomerate  to  very  coarse  conglomerate  seems  to  be  here  more  sudden. 

PARADISE   COARSE  CONGLOMERATES. 

PARADISE    ROCKS. 

The  continuous  exposures  of  the  coarse  conglomerates  forming  the 
eastern  side  of  Eastons  Point  terminate  northward  at  Sachuest  Beach. 
The  same  series  farther  northward  forms  the  Paradise  Rocks.  The  lower 
beds  of  the  conglomerate  series  are  exposed  a  third  of  a  mile  north  of  the 
beach,  west  of  the  road,  near  a  stream.  They  are  chiefly  sandstone,  with 
a  few  conglomerate  layers;  strike  N.  12°  E.,  dip  70°  E.  Farther  east, 
just  west  of  the  road,  there  are,  almost  in  situ,  very  large  conglomerate 
bowlders,  with  large  pebbles,  forming  the  base  of  the  coarse  conglomerates. 


296  GEOLOGY  OF  THE  NARRAGANSETT  BASIN, 

The  sandstone  beneath  the  conglomerates  is  again  exposed  five-sixths  of  a 
mile  north  of  the  beach,  an  eighth  of  a  mile  east  of  the  road,  north  of 
a  farmhouse.  Here  it  is  a  bluish  sandstone  and  dips  about  40°  E.  The 
basal  conglomerate  not  far  eastward  dips  60°  E. 

Almost  the  entire  thickness  of  the  coarse  conglomerates  exposed  at  the 
western  Paradise  Rocks  belongs  unquestionably  to  a  single  eastward-dipping 
series,  combining  northward  to  form  the  higli  ridge  Avhich  is  the  conspicu- 
ous element  of  the  landscape.  At  the  more  southern  exposures  west  of  the 
reservoir  the  conglomerate  beds  form  a  series  of  parallel  ridges  in  the  fields; 
strike  N.  18°  E,,  dip  east.  Noi'thward,  the  second  field  containing  exposures 
shows  a  dip  of  60°  E.  in  one  of  the  middle  ridges;  this  dip  is  better 
shown  southeast  of  a  house.  The  most  eastern  ridge,  forming  a  steep  cliff" 
bordering  the  reservoir,  has  coarse  conglomerate  dipping  40°  to  46°  E. 
Passing  northward  out  of  the  grounds  immediately  surrounding  the  Bel- 
mont House,  the  naore  western  conglomerates  form  the  southern  end  of  the 
high  conglomerate  ridge,  to  which  reference  has  already  been  made,  dipping 
50°  E.  on  the  west  side  and  60°  E.  on  the  east  side,  while  the  contin- 
uation of  the  conglomerate  bed,  bordering  the  reservoir,  still  dips  45° 
E.  Farther  north  the  bluish  sandstone  beneath  the  conglomerate  series, 
already  described,  dips  40°  E.  The  most  western  conglomerate  exposures 
dip  60°  E.  Farther  uj)  the  conglomerate  ridge  the  dip  becomes  80°  E., 
diminishing  on  the  east  side  to  about  40°  E.  on  the  northward  continua- 
tion of  the  conglomerate  which  farther  southward  borders  the  reservoir. 
Northward,  at  the  quarry  on  the  west  side  of  the  main  ridge,  the  dip  has 
diminished  to  45°  or  50°  E.,  and  as  the  strike  swings  eastward  so  as  to 
become  N.  30°  E.,  the  dip  on  the  eastern  side  diminishes  for  a  long  distance 
to  30°  E. 

These  exposures,  with  easily  recognized  eastward  dip,  terminate  at 
an  east-west  field  wall  about  a  third  of  a  mile  south  of  the  east-west 
road  bordering  the  Paradise  tract  on  the  north  side.  East  of  the  last 
exposure  with  marked  eastward  dip,  and  east  of  its  line  of  strike,  the 
exjjosure  north  of  the  fence  shows  an  almost  vertical  dip,  or  80°  W. 
Eastward,  in  the  field,  a  dip  of  50°  E.  was  noticed.  A  short  distance  to 
the  southeast  of  these  exposures,  and  east  of  their  line  of  strike,  the  second 
and  more  eastern  ridge  of  the  Paradise  Rocks  begins.  At  its  north  end  the 
dip  is  70°  to  80°  E.     This  continues  southward,  as  well  as  can  be  deter- 


PARADISE  ROOKS.  297 

mined,  notwithstanding  evidence  of  some  degree  of  folding.  A  subsidiary 
ridge  west  of  the  main  line  of  outcrop  shows  almost  vertical  dips — 80°  E. 
on  the  east  side,  80°  W.  on  the  west  side — owing  to  a  moderate  diver- 
gence of  the  bedding  planes  of  the  two  extreme  layers.  Southeastward 
the  main  line  of  outcrop  begins  again,  with  a  dip  of  85°  W.,  and  this 
nearly  vertical  dip  is  maintained  for  some  distance  south,  becoming  70° 
W.  at  the  most  southern  exposure,  between  the  middle  and  western  streams 
entering  the  reservoir. 

A  very  important  point  should  here  be  noted.  While  the  mass  of  con- 
glomerates forming  the  western  and  higher  eastward-dipping  Paradise 
Ridge  is  of  considerable  thickness,  that  forming  the  lower  and  practically 
vertical-dipping  eastern  ridge  is  only  one-third  or  one-fourth  as  thick. 
So  that,  although  a  synclinal  structure  might  be  imagined  between  these 
two  ridges,  there  is  not  as  much  conglomerate  exposed  on  the  east  side 
of  the  supposed  syncline  as  would  be  expected  in  the  case  of  such  a 
structure.  Another  equally  important  point  is  this:  A  continuation  of  the 
line  of  strike  of  the  more  eastern  Paradise  Ridge  would  reach  a  solitary 
coarse  conglomerate  exposure  at  the  west  end  of  Sachuest  Beach,  with 
strike  N.  14°  E.,  which  has  a  dip  of  40°  E.,  but  in  order  to  agree  with 
the  synclinal  structure  demanded  northward  its  dip  ought  to  be  west.  Less 
important,  because  the  exposures  are  not  equally  satisfactory,  is  the  vertical 
dip  shown  by  the  exposure  east  of  the  north  end  of  the  continuous  eastward- 
dipping  line  of  exposures  already  described,  where  the  dip  is  50°  E.  The 
dip  of  the  more  eastern  exposure  should  be  westward  to  agree  with  synclinal 
structure  in  this  region.  The  second,  more  eastern,  ridge  shows  in  places 
evidences  of  local  folding. 

In  view  of  all  the  facts  observed  it  seems  reasonable  to  suppose  that  the 
Paradise  ridges  form  a  great  eastward-dipping  series  of  conglomerates  on 
the  western  side  of  a  syncline.  The  eastern  of  the  two  ridges  dips  east- 
ward only  at  the  southern  end.  North  of  the  reservoir  the  conglomerate 
beds  of  this  eastern  ridge  are  affected  by  a  local  flexure  traversing  the 
series  a  little  diagonally,  which  has  bent  these  beds  downward  and  moder- 
ately overturned  them  northward,  so  that  the  almost  vertical  but  somewhat 
westward  dip  of  the  eastern  ridge  along  its  southern  end  is  changed  to  an 
almost  vertical  but  slightly  eastward  dip  near  its  northern  end,  the  dip  of 
50°  E.  in  the  field  a  considerable  distance  north  of  the  second  ridge,  and 


298  GEOLOGY  OF  THE  NARRAGANSETT  BASIN. 

another  of  40°  E.  on  Sachuest  Beacli,  south  of  the  ridge,  remaining  to  show 
the  real  structure  of  the  series  of  which  this  eastern  ridge  forms  a  part. 

At  the  north  end  of  the  western  or  principal  ridge  the  lower  eastward 
dips  show  that  the  syncline  is  more  shallow  northward.  The  low  dips 
seem  to  continue  northward,  since  the  remaining  conglomerate  exposures 
as  far  as  the  east-west  road  fail  to  bring  up  on  end  the  interbedded  sand- 
stones, and  so  their  dip  can  not  be  determined.  North  of  the  road,  how- 
ever, in  a  field  a  fifth  of  a  mile  west  of  the  road  corners,  conglomerate  is 
exposed  with  a  strike  N.  30°  E.,  dip  20°  E.,  lower  eastward.  North  of  the 
road  corners  above  mentioned  blue  sandstone  with  a  little  conglomerate 
dips  low  eastward,  and  seems  to  pitch  southward.  A  sixth  of  a  mile  south- 
ward, west  of  the  angle  of  the  road,  similar  sandstone  is  exposed  in  a  field. 

HANGI^TG  KOCKS. 

The  Hanging  Rocks,  along  the  western  side  of  Grardners  Pond,  form 
the  southern  end  of  another  great  ridge  of  coarse  conglomerate.  The  strike 
of  the  conglomerate  in  the  ridge  is  N.  16°  E.,  dip  70°  W.,  in  some  places 
almost  vertical.  Overlying  it  on  the  western  side,  noi'thward,  is  a  bluish,  in 
places  shaly,  sandstone.  This  Hanging  Rock  ridge  of  conglomerate  is 
about  half  a  mile  long.  It  seems  to  form  the  eastern  side  of  a  great 
southward-pitching  syncline,  of  which  the  Paradise  Rocks  form  the  western 
side.  Seen  from  one  of  the  g-reat  trap  ridges  in  the  central  area  of  this 
synclinal  district,  the  topography  favors  such  an  interpretation  of  the  series. 
Immediately  east  of  Hanging  Rock,  north  of  the  bend  at  which  the  road 
skirting  it  turns  eastward,  a  low  ridge  of  conglomerate  is  found,  west  of 
the  brook.  Its  dip  seems  to  be  steep  eastward,  nearly  vertical.  Other 
exposures  are  found  farther  northward,  west  of  the  brook.  East  of  the 
brook  is  another  low  conglomerate  ridge  extending  southward  into  Gardners 
Pond  and  forming  the  eastern  border  of  the  narrow  division  of  the  pond 
into  which  the  brook  empties.  The  strike  of  the  main  exposure  here  on 
the  west  side  is  N.  16°  E.,  dip  from  80°  W.  to  vertical.  The  fact  that 
this  exposure  lies  east  of  the  line  of  strike  of  the  exposures  farther  north, 
on  the  west  side  of  the  brook,  which  sometimes  show  eastward  dips,  should 
be  noted.  Along  the  eastern  side  of  this  promontory,  near  its  southern 
end,  the  dip  is  about  60°  E.  This  eastward  dip  continues  to  be  shown 
by  the  continuation  of  the  eastern  side  of  this  line  of  exposure  northward, 
being  40°  E.  in  the  fields  north  of  the  road,  the   strike  being  N.  20°  K. 


HANGING  EOOKS.  299 

East  of  the  strike  of  this  line  of  outcrops,  at  its  northern  end,  west  of  a  farm- 
house, is  another  exposure  of  conglomerate  stx-iking  N,  10°  E.,  but  dipping 
80°  E.,  and  insignificant  exposures  are  found  southward  from  this  last 
exposure. 

If  now  the  series  of  exposures  east  of  the  main  Hanging  Rock  ridge 
be  taken,  and  their  dips  be  compared,  it  will  be  seen  that  there  is  a  succes- 
sion of  steep,  practically  vertical,  and  of  less  inclined,  eastward  dips.  This 
might  at  first  sight  be  taken  as  evidence  of  a  series  of  anticlines  and  syn- 
clines.  But  the  ridge  occuiTing  immediately  east  of  the  brook  which 
empties  southward  into  the  pond,  changes  from  a  steep,  practically  vertical 
dip  near  its  southern  end  to  a  lower  eastward  dip  on  going  northward,  and 
also  to  a  lower  eastward  dip  on  going  southeast  to  the  edge  of  the  promon- 
tory on  the  pond.  East  of  the  northeast  end  of  this  ridge  east  of  the  brook 
the  steep  eastward,  nearly  vertical  dip  comes  in  again.  It  is  believed  that 
these  conglomerates  are  not  folded  in  anticlines  and  synclines,  but  that  all 
form  parts  of  a  steeply  west-dipping  series  affected  by  flexures  varying  as 
regards  the  dip  along  the  strikes  of  the  same  beds,  and  apparently  also  vary- 
ing in  this  regard  in  closely  contiguous  beds.  This  is  a  condition  of  things 
not  infrequently  seen  when  a  general  synclinal  structure  has  been  brought 
about  in  a  series  of  harder  rock  separated  by  layers  of  softer  material^ 
which  permit  of  more  or  less  sliding.  Structures  of  this  kind  may  be  seen 
on  a  smaller  scale  in  connection  with  the  folding  at  the  north  end  of 
Sachuest  Neck.^ 

The  Hanging  Rocks  and  more  eastern  exposures  are  believed  to  be 
the  eastern  side  of  a  great  syncline,  of  which  the  Paradise  Rocks  form  the 
western  side.  The  folding  of  the  Easton  Point  anticline  on  the  west  side 
of  this  syncline  is  quite  regular,  and  hence  the  eastern  side  of  this  syncline, 
which  forms  the  western  side  of  the  Paradise-Hanging  Rock  syncline,  pre- 
sents quite  regularly  only  the  eastward  dips,  except  along  the  eastern  ridge, 
where  very  steep  westward  dips  occur  in  places,  as  described.  The  anti- 
cline on  the  eastern  side  of  the  Pai'adise-Hanging  Rock  syncline  is 
evidently  the  result  of  stronger  folding,  the  dips  from  Smiths  Beach  to 
Taggarts  Ferry  being  often  70°  E.,  and  at  the  ferry  vertical  or  80°  W. 

'  Dale,  Crosby,  and  Barton  regard  the  structure  of  the  Hanging  Rocks  district  as  an  anticline. 
The  conglomerate  east  of  tbe  Hanging  Eoclis  dips  east,  while  the  Hanging  Rocks  dip  west.  This 
interpretation  would  demand  the  assumption  that  but  a  small  part  of  the  conglomerate  on  the  western 
side  of  tlie  anticline  is  actually  exposed. 


300  GEOLOGY  OF  THE  NAREAGANSETT  BASIN. 

On  the  west  side  of  the  Woods  Castle-Black  Point  anticline  the  series  in 
the  Hanging  Rocks  Valley  is  evidently  somewhat  overturned  in  places, 
although  the  chief  ridge,  that  of  the  Hanging  Rocks,  dips  80°  W.  The 
result  of  the  more  accentuated  folding,  as  indicated  by  the  steeper  dips,  is 
a  violent  contortion  of  the  rocks,  shown  by  the  local  rapid  variation  of  dip, 
due  to  local  folding  subsidiary  to  the  more  general  synclinal  folding  which 
determined  the  great  structural  features  of  the  Carboniferous  area  along 
the  Hanging  Rock  Valley  and  Avestward.  This  syncline  is  believed  to 
pitch  strongly  southward. 

The  most  northern  outcrops  of  coarse  conglomerate  occur  a  little  over 
a  mile  from  both  Black  Point  and  Taggarts  Ferry,  about  three-quarters  of 
a  mile  west  of  the  Sakonnet  River,  along  the  west  and  east  sides  of  the 
road.  Here  the  strike  is  N.  3°  E.,  dip  46°  W.,  on  the  east  side  of  the 
road  southward,  changing  to  strike  N.  15°  E.,  dip  40°  E.,  on  the  west  side 
of  the  road  near  the  middle  exposure,  and  dipping  the  same  amount  east  at  a 
continuation  of  the  middle  exposure  northward  on  the  east  side  of  the 
road.  This  seems  to  represent  the  northern  end  of  the  syncline  in  the 
coarse  conglomerate  bed,  and  lies  about  60  to  80  feet  above  sea  level. 
Southward  the  base  of  the  syncline  pitches  far  beneath  sea  level. 

PRB-CARBONIFEROUS  AREA. 

Between  the  eastern  ridge  of  the  Paradise  conglomerates  and  the 
Hanging  Rock  ridge  of  conglomerate  lies  an  area  of  igneous  rock  and  of 
quartzite-schists  which  seems  to  be  pre-Carboniferous.  The  most  south- 
western exposure  of  the  hornblendic  rock,  possibly  at  the  time  of  its  injection 
a  coarse  diabase,  is  found  along  the  southern  embankment  of  the  reservoir, 
at  an  angle  near  its  middle  line.  The  next  exposure  occurs  at  the  northern 
end  of  the  reservoir,  between  the  middle  and  the  eastern  creeks  entering  the 
reservoir  from  that  side.  It  there  forms  a  ridge  which  can  be  traced  north- 
ward for  about  half  a  mile,  and  is  evidently  in  line  with  the  exposure  south 
of  the  reservoir.  Bordering  the  east  side  of  the  reservoir  is  another,  much 
loftier  and  broader  range  of  the  igneous  rock,  almost  half  a  mile  long. 
East  of  this  lies  a  somewhat  narrower  ridge,  at  one  point  broken  down  and 
permitting  the  formation  of  a  glen  between  the  main  range  of  igneous  rocks 
westward  and  another  high  ridge  lying  to  the  eastward.  This  eastern  ridge 
lies  directly  west  of  the  Hanging  Rock  coarse  conglomerate  with  its  over- 
Ivino-  bluish  sandstone  and  more  arreenish  shalr  varietv. 


PKE  OAliBO^IFEEOUS  EOCKS  OF  PARADISE.  301 

The  igneous  rock  has  evidently  penetrated  a  great  mass  of  quartzitic 
schists  similar  to  those  foxind  west  of  East  Greenwich,  north  of  Tiverton, 
south  of  Common  Fence  Point,  and  elsewhere,  and  to  a  somewhat  less 
degree  like  the  quartzitic  schists  or  shales  east  of  Browns  Point.  These 
schists  may  be  found  well  exposed  in  the  area  between  the  two  main  ranges 
of  the  igneous  rock  east  of  the  pond  and  on  the  promontory  between  the 
middle  and  east  creeks  north  of  the  reservoir.  They  were  formerly  also 
well  exposed  on  an  island  in  the  southeastern  corner,  now  covered  by  the 
reservoir.  They  occur  also  as  fragments  inclosed  in  the  larger  ridges  of  the 
igneous  rock  and  in  the  smaller  exposures  of  the  same  material.  Curiously 
the  strike  and  dip  of  the  included  fragments  and  of  the  larger  masses  of 
the  quartzitic  schist  penetrated  by  the  trap  dikes  are  so  constant  that  a  gen- 
eral strike  of  N.  20°  E.  and  a  dip  of  50°  to  60°,  sometimes  70°,  W.  will 
sufficiently  explain  their  general  relations  to  one  another.  On  the  promon- 
tory of  trap  rock  north  of  the  pond,  however,  it  may  be  seen  that  this  strike 
is  chiefly  the  direction  of  the  plane  of  schistosity,  the  bedding  being  appar- 
ently, at  least  in  places,  at  variance  with  the  same. 

The  igneous  rock  above  referred  to  as  cutting  the  pre-Carboniferous 
whitish  quartzitic  rocks  in  the  Paradise-Hanging  Rock  region  shows,  even 
macroscopically,  the  presence  of  a  crystalline  structure.  The  rock  is 
composed  chiefly  of  plagioclase  and  hornblende,  both  in  a  very  advanced 
state  of  decomposition.  This  combination  would  place  the  rock  under  the 
heading  of  diorite,  and  here  it  is  placed  by  Mr.  George  P.  Merrill,  who 
first  made  a  microscopical  examination  of  these  dike  rocks.  He  makes, 
however,  the  qualification  that  "it  is,  of  course,  possible  that  this  horn- 
blende may  itself  be  secondary  and  that  the  perfectly  fresh  rock  would 
show  augite;  but  this  does  not  seem  probable."  If  hornblende  replaced 
original  augite,  the  trap  rock  would  then  be  an  altered  diabase. 

With  this  determination  of  the  igneous  character  of  the  trap  rocks  of 
the  Paradise-Hanging  Rock  region  in  hand,  Professors  Crosby  and  Barton^ 
were  the  first  to  make  a  careful  study  of  these  dikes,  and  they  state  that  in 
no  instance  did  the}^  "  discover  the  slightest  indication  of  a  passage  from 
the  dike  rock  to  the  [quartzitic]  slate,  but  the  two  are  always  separated  by 
a  perfectly  sharp  and  definite  line." 

The  trap  occurs  in  parallel  ridges  running  in  the  same  direction  as  the 

1  Proc.  Boston  Soc.  Nat.  Hist.,  Vol.  XXIII,  1886,  p.  32.5  et  seq. 


302  GEOLOGY  OF  THE  NARRAGANSETT  BASIN. 

coarse  conglomerate  ridges.  The  largest  of  these  are  on  the  eastern  side  of 
the  region  here  described.  The  great  ridge  west  of  the  Hanging  Rock 
ridge  is  composed  almost  entirely  of  trap,  but  shows  toward  the  north,  on 
its  eastern  face,  toward  the  upper  portion  of  the  ridge,  a  number  of  long 
inclusions  of  the  quartzitic  slate  which  it  in  general  intersects.  This 
quartzitic  rock  is  also  shown  on  the  western  side  of  the  same  trap  ridge, 
near  its  highest  elevation;  it  also  is  exposed  on  the  eastern  side  of  the  next 
ridge  westward,  and  probably  once  occupied  the  valley  separating  the 
two  ridges.  This  western  ridge  is  also  composed  almost  entirely  of  trap 
rock,  the  dike  rock  forming  the  top  and  the  entire  western  face  of  the 
ridge.  Toward  the  north  a  lower  ridge  of  trap  is  found  between  the 
other  two.  West  of  the  western  of  the  lofty  trap  ridges  is  the  reservoir. 
At  a  very  low  stage  of  the  water  in  the  reservon  an  island  is  exposed 
which  is  composed  chiefly  of  the  quartzitic  sandstone,  but  which  also 
shows  trap  on  the  western  side.  Crossing  the  eastern  brook  entering  the 
reservoir  from  the  north,  a  trap  dike  is  encountered,  then  quartzitic  slate, 
then  more  trap.  Northward  these  trap  exposures  increase  in  elevation 
and  form  the  eastern  side  of  a  low  ridge  lying  approximately  along  the 
middle  of  the  reservoir  valley.  Near  the  northern  end  of  this  region 
inclusions  of  the  quartzitic  slate  can  be  seen  in  the  trap.  The  slate  is  found 
also  west  of  this  trap  ridge. 

The  Paradise-Hanging  Rock  valley  is  undoubtedly  occupied  alto- 
gether b}^  the  quartzitic  slate,  intersected  by  coarse  trap,  the  quartzitic  slate 
forming  the  valleys  and  the  trap  the  ridges.  . 

In  the  present  state  of  knowledge  on  the  subject,  no  place  for  these 
quartzitic  schists  can  be  found  in  the  Carboniferous  series.  They  either 
overlie  or  underlie  these  rocks,  and  owing  to  their  resemblance  to  rocks  else- 
where with  confidence  adjudged  pre-Carboniferous,  they  are  also  considered 
older  than  Carboniferous,  and  are  believed  to  have  been  left  as  a  great 
triangular  mass,  bounded  east  and  west  by  fault  planes  along  which  the 
Carboniferous  strata  dropped  down.  Whether  the  diabasic  rock  preceded 
or  anteceded  the  period  of  deposition  of  Carboniferous  rocks  is  not  known. 
Attention  should,  however,  be  drawn  in  this  connection  to  the  frequency  of 
dike  action  in  the  pre-Carboniferous  shales  of  the  Newport  Neck  region, 
and  to  a  less  degree  in  the  green  pre-Carboniferous  rocks  of  Sachuest  Neck 
and  in  the  Conanicut  Carboniferous  shale  series. 

All  of  these  interpretations  of  the  geological  structure  of  the  exposures 


EASTONS  POND.  303 

of  the  Paradise  and  Hanging  Rock  series  may  seem  rather  forced,  but  they 
appear  to  be  the  only  ones  consistent  with  knowledge  obtained  elsewhere 
in  the  field,  which  rests  on  a  more  secure  foundation.  No  eff'ort  has  been 
spared  to  secure  a  more  ready  and  simple  explanation,  but  the  exposures 
are  not  sufficiently  numerous  and  conclusive,  and  the  interpreter  is  di-iven 
to  theorizing  where  more  exposures  would  make  this  unnecessary.^ 

ISOLATED    CONGLOMERATE    EXPOSURES    NEAR  EASTONS    POND  AND 

NORTHWARD. 

On  the  west  side  of  the  Eastons  Point  anticline  it  will  be  remembered 
that  there  is  evidence  of  synclinal  structure,  and  that  at  the  east  end  of 
Eastons  Beach  the  dip  is  about  15°  to  20°  E 

West  of  the  northern  half  of  Eastons  Pond,  below  the  greenhouses, 
bluish  sandstone,  darker  shaly  rock,  and  some  conglomeratic  layers  com- 
posed of  pebbles,  not  recalling  the  coarse  conglomerate  series,  are  found. 
They  do  not  seem  to  vary  far  from  a  horizontal  position. 

Three-quarters  of  a  mile  northward,  in  the  field,  north  of  a  farmhouse 
north  of  the  east-west  road,  much  coarser  conglomerate  is  exposed,  with 
quartzitic  pebbles  of  the  Paradise  Rock  type  up  to  8  inches  in  length,  but 
usually  only  3  to  4  inches  long.  It  seems  to  be  part  of  an  anticlinal  fold 
pitching  northward  about  10°  and  trending  N.  16°  E.  On  the  western 
side  the  dip  is  about  15°  W. 

A  somewhat  similar  conglomerate  is  exposed  a  mile  northeastward, 
west  of  the  western  road  corners  of  a  triangular  plat  of  land  formed  by  the 
public  ways.  The  pitch  here  seems  to  be  also  low  northerly,  the  strike 
being  apparently  N.  7°  W.,  dip  very  low  west,  but  the  exposure  is  not 
suitable  for  the  exact  determination  of  these  features. 

The  precise  relation  of  these  exposures  to  the  general  shale  series 
northward  and  westward  is  not  known. 

According  to  the  interpretation  given  by  Professor  Dale  (loc.  cit.),  the 
great  Purgatory  conglomerates  overlie  the  Aquidneck  shale  series,  but  dip 
under  the  Newport  Cliff  exposures.  To  the  writer  the  cliff  exposures  appear 
to  belong  to  the  horizon  of  the  Sakonnet  sandstones  and  the  lower  half  of 
the  Purgatory  conglomerates,  though  he  does  not  know  of  any  very  con- 
clusive evidence  for  either  view. 


'  Consult,  on  the  same  area,  T.  Nelson  Dale,  Boston  See.  Nat.  Hist.,  Vol.  XXII,  1883,  and  Proc.  New- 
port Soc.  Nat.  Hist.,  1885. 


304  GEOLOGY  OP  THE  NAKRAGANSETT  BASIN. 

MIANTONOMY     HILL     AND     COASTERS    HARBOR     ISLAND     CONGLOM- 
ERATES. 

MIANTONOMY    HILL. 

A  little  over  a  quarter  of  a  mile  south  of  the  top  of  Miantonomy  Hill 
coarse  conglomerate  is  exposed,  south  of  a  house  along  the  edge  of  a  field. 
It  is  again  exposed  northwest  of  the  house,  trending  northward.  Northward 
it  forms  the  entire  structure  of  Miantonomy  Hill.  Interbedded  sandstone 
along  the  entire  northern  margin  of  the  hill  shows  the  conglomerate  to  be 
apparently  horizontal  from  east  to  west,  but  in  fact  dipping  southward  at  an 
angle  of  about  15°.  There  is  apparently  a  low  eastward  dip  at  the 
northeast  angle  of  the  hill. 

The  pebbles  of  this  conglomerate  are  of  the  largest  size,  at  times  more 
than  2  feet  long,  and  they  have  not  been  elongated.  They  are  evidently  of 
the  Purgatory  type. 

Northward,  between  Miantonomy  and  Beacon  hills,  there  is  exposed 
considerable  dark-blue  sandstone,  shaly  in  places,  dipping  low  southward. 

BEACON    HILL. 

On  the  summit  of  Beacon  Hill  more  conglomerate  is  exposed.  The 
pebbles  on  the  average  are  of  much  smaller  size  and  usually  do  not  exceed 
8  inches  in  diameter.  The  series  has  evidently  been  slightly  folded  by 
an  east-west  thrust,  as  may  readily  be  detected  by  following  the  line 
between  the  conglomerate  and  the  overlying  interbedded  sandstone  at  the 
north  end  of  the  hill  summit.  The  pitch  is  again  about  15°  S.,  and  the 
westward  dip  on  the  northwest  side  of  the  hill  suggests  that  the  conglomer- 
ate is  here  descending  into  the  valley.  The  conglomerate  of  Beacon  Hill 
evidently  underlies  the  much  coarser  conglomerate  of  Miantonomy  Hill. 

FIELD    EXPOSURES. 

In  a  field  west  of  Miantonomy  Hill  and  just  east  of  the  railroad  is  a 
series  of  coarse  conglomerate  exposures,  striking  N.  8°  W.  and  dipping 
45°  E.  The  most  western  exposure  has  smaller  pebbles,  the  more  eastern 
ones  larger  pebbles,  some  of  these  attaining  a  length  of  IJ  to  2  feet. 
Fossil  oboli  were  found  in  one  of  the  pebbles.  Interbedded  sandstones 
disclose  the  dip.     This  dip  indicates  a  synclinal  structure  between  these 


CODD]NGT0:tT  iSTECK.  305 

exposures  and  those  of  Miantonomy  and  Beacon  hills.  The  southward 
pitch,  so  well  shown  on  the  hills  named,  indicates  how  it  is  possible  to  have 
the  regular  dark-blue  and  black  shale  along  the  railroad  cut  north  and 
south  of  Coddington  Cove  along  with  a  total  disappearance  of  the  conglom- 
erate series.  Anyone  standing  on  the  top  of  Beacon  Hill,  and  knowing 
the  distribution  of  the  shale  series  northward,  can  not  fail  to  be  convinced 
that  the  coarse  conglomerates  overlie  that  series. 

CODDINGTON    NECK. 

The  bluish-black  shale  series  underlies  Coddington  Neck.  Almost 
continuous  exposures  occur  along  the  western  side  of  Coddington  Cove,  and 
form  the  two  main  hills  of  the  neck.  At  tlie  north  end  of  the  neck  these 
shales  strike  N.-S.  and  dip  70°  .to  80°  W.  Farther  west  these  dips  are 
less  steep.  About  225  feet  southwest  of  the  most  northern  point  of  the 
neck  fern-leaf  impressions  Avere  found  in  the  bluish-black  shale.  At  the 
northwestern  angle  of  the  neck  coarse  conglomerate  appears,  still  dipping 
westward,  overlying  conglomerate  with  medium-sized  pebbles.  Farther 
along  the  coast  southwestward,  more  conglomerate  with  medium-sized 
pebbles  is  seen;  then  brownish  sandstone,  again  the  former  conglomerate, 
and  then  coarse  conglomerate  appear  in  succession,  the  second  exposure  of 
coarse  conglomerate  appearing  at  the  western  angle  of  the  shore  where  it 
begins  to  turn  southward.  The  dip  of  the  coarse  conglomerate  here  is  very 
steep  eastward.  In  other  words,  a  very  compressed  syncline  has  brought 
down  the  base  of  the  coarse  conglomerate  series.  Southward  from  the 
more  southern  conglomerate  exposure,  the  bluish-black  shale  series  is  seen 
to  contain  frequent  narrow  intercalations  of  a  whitish  sandy  rock. 

BISHOP    ROCK. 

The  same  series  of  blue-black  and  coaly  black  shales,  with  bands  of 
whiter  rock,  is  exposed  on  the  northwest  side  of  Bishop  Rock,  striking  N. 
40°  E.  on  the  north  side,  toward  Coddington  Neck,  and  curving  westward 
and  then  southward  so  as  to  strike  about  N.  25°  E.  on  the  west  side  of  the 
rock.  The  series  dips  westward  about  60°.  Underlying  it,  southeastward, 
is  medium.-sized  quartzitic  conglomerate,  and  beneath  that  is  coaly  shale, 
evidently  much  folded  and  contorted.  Fragments  of  arkose  and  other 
rocks  appear    in  the  coaly  shale  as  though  they  were  pebbles,  but  the 

MON  XXXIII 20 


306  GEOLOGY  OF  THE  NAEEAGAXSETT  BASIN. 

appearance  of  some  of  the  larger  fragments  suggests  that  they  once  formed 
continuous  beds  intercahxted  in  the  coaly  shale.  In  that  case  the  occur- 
rence of  arkose  in  this  shale  is  of  interest.  It  will  be  remembered  that 
arkose  is  associated  with  coaly  shales  on  Sachuest  Neck.  It  is  beheved 
there  to  overlie  a  greenish  shale  and  conglomerate,  possibly  comparable 
with  the  Little  Compton  green  shales.  It  derived  the  materials  for  the 
arkose  in  part  from  the  coarse-grained  granites  on  the  south  and  east. 

The  granite  nearest  to  Bishop  Rock  is  2^  miles  distant,  at  the  southern 
end  of  Jamestown,  on  Conanicut,  and  at  the  southern  end  of  Newport  Cliffs 
and  on  the  adjacent  part  of  the  neck.  The  nearest  exposures  of  green 
shales  are  on  Goat  Island,  Rose  Island,  and  Freebody  Hill.  Nowhere 
can  these  rocks  be  brought  in  close  relation  with  one  another  so  that  their 
relative  age  may  be  determined.  The  arkose  on  Bishop  Rock  seems  to 
belong  to  a  horizon  not  far  from  the  coarse  conglomerate  on  the  western 
side  of  Coddington  Neck,  and  probably  occur  just  beneath  the  same.  Simi- 
lar arkose  occurs  near  the  southern  end  of  Coasters  Harbor  Island. 

COASTERS  HARBOR  ISLAND. 

The  very  coarse  conglomerates,  with  pebbles  often  1  foot  and  at  times 
2  feet  long,  so  well  shown  on  Miantonomy  Hill,  are  again  well  shown  on 
Coasters  Harbor  Island.  No  elongation  of  the  pebbles  is  observable  here. 
The  strikes  and  dips  are  variable.  The  most  southern  exposure  of  conglom- 
erate on  the  east  side  of  the  island  has  a  strike  N.  65°  E.,  dip  40°  to  50° 
NW.  North  of  a  small  indentation  of  the  coast  the  strike  remains  N.  65° 
E.,  but  the  dip  becomes  only  20°  NW.  Within  a  short  distance  north- 
ward the  strike  changes  to  N.  80°  W.  and  the  dip  becomes  60°  NE.,  and 
along  the  northeast  coast  the  strike  is  N.  30°  W.  and  at  various  locah- 
ties  the  dip  is  80°  to  85°  E.  West  of  a  small  embayment  the  rocks  of  the 
northern  promontory  of  the  island  seem  to  be  in  part  folded,  and  elsewhere 
dip  80°  W.,  striking  N.  10°  E.  In  an  embayment  west  of  this  promon- 
tory sandstone  is  exposed,  the  apparent  dip,  which  may  be  cleavage,  strik- 
ing N.  35°  E.,  dip  southward.  At  the  northwest  angle  of  the  island  the 
strike  is  N.  30°  E.,  curving  southward  to  N.  10°  E.  and  N.-S.,  while 
the  dip  is  constantly  eastward,  about  40°  E.  northward,  becoming  less 
southward.  Southward  carbonaceous  sandstone  and  fine  conglomerate  are 
faulted  against  the  coarse   conglomerate,  which  is  almost  horizontal,  and 


NEWPORT  HARBOR  ISLANDS.  307 

then  the  strike  suddenly  becomes  N.  80°  W.,  dip  40°  S.,  changing  to  N.  20° 
W.,  dip  irregularly  south,  after  which  carbonaceous  shales  and  sandstones 
make  their  appearance,  occasionally  showing  conglomerate,  the  strike  being 
approximately  N.-S.,  and  the  dip  45°  E.  Southward,  along  the  southwestern 
border  of  the  main  body  of  the  island,  coarse  conglomerate  is  seen  again, 
striking  at  first  N.  40°  E.,  dip  40°  to  20°  E.;  then,  as  the  shore  turns  southeast, 
the  strike  becomes  N.  45°  W.,  then  N.  10°  W.,  dip  low  east,  the  conglom- 
erate becoming  less  coarse.  Farther  southward  dips  of  30°  E.  are  noticed, 
and  then,  as  the  shore  turns  southward,  green  fissile  shales,  similar  to  the 
Conanicut  shales,  make  their  appearance. 

At  the  southwest  angle  of  this  tongue  of  the  island,  arkose  with  thin 
layers  of  carbonaceous  shale  outcrop,  with  strike  E.-W.,  dip  40°  N.  The 
rock  south  of  the  arkose  and  forming  the  southern  end  of  the  island  is 
a  greenish  rock,  which  provisional^  is  here  placed  with  the  Newport  Neck 
series  of  shales.  Near  the  arkose  it  strikes  N.  30°  W.,  dip  40°  E.,  and  east- 
ward N.  50°  W.,  dip  25°  E.  Similar  arkose  is  found  on  Bishop  Rock  and 
on  Rose  Island. 

The  coarse  conglomerates  of  Coasters  Harbor  Island  are  evidently  to 
be  associated  with  the  Miantonomy  Hill  conglomerate.  The  occurrence  of 
almost  constant  eastward  dips  along  the  western  side  of  the  island  is  to  be 
emphasized.  The  discussion  as  to  the  relationship  of  these  conglomerates 
to  the  green  shales  at  the  south  end  of  the  island  is  deferred  until  the 
Harbor  Islands  are  taken  up. 

NEWPORT  HARBOR  ISLANDS. 

In  this  connection  the  description  of  the  occurrence  of  the  green  shales 
at  the  southern  end  of  Coasters  Harbor  Island  should  be  again  noted.  Off 
the  shore  to  the  south  of  the  island  additional  exposures  of  the  green  shales 
occur.     They  are  considered  to  be  of  pre-Carboniferous  age. 

GULL  ROCKS. 

The  main  rock  is  occupied  by  a  light-house.  The  pre-Carboniferous 
green  shale  here  includes  a  more  sandy,  coarser  variety  of  that  rock,  dipping 
about  20°  N.  A  short  distance  southward  is  another  exposure  of  similar 
nature,  also  dipping  northward. 


308  GEOLOGY  OF  THE  iS^ARRAGANSBTT  BASIK 

ROSE  ISLAND. 

The  main  body  of  Rose  Island,  all  except  the  narrow  tongue  projecting 
northward,  is  composed  of  the  greenish  rock  already  mentioned  as  occurring 
on  the  Gull  Rocks  anc"  at  the  south  end  of  Coasters  Harbor  Island.  The 
strike,  as  heretofore,  is  approximately  E.-W.,  the  dip  15°  to  20°  N. 
Some  of  the  layers  are  coarser  and  resemble  sandstone,  while  others  are 
tinted  purplish,  as  at  Gull  Island  light-house.  They  are  considered  to  be 
of  pre-Carboniferous  age. 

North  of  the  green  series  of  rocks  on  the  eastern  side  of  Rose  Island 
arkose  appears.  It  seems  to  strike  north-south  and  dips  almost  vertically. 
Farther  north,  forming  the  lunate  extension  of  the  tongue,  are  (ioaly  sand- 
stone and  shale,  with  strike  N.  25°  E.  and  very  steep  dip,  perhaps  70°  W. 
On  the  western  side  arkose  layers  occur  also  southward  toward  the  contact 
with  the  green  shales,  green  shales  coming  in  contact  with  the  arkose  as 
though  brought  together  by  a  fault.^  Reference  has  already  been  made  to 
the  arkose  on  Bishop  Rock  and  Coasters  Harbor  Island. 

CONANICUT    ISLAND. 

The  arkose  northwest  of  the  granite  area  east  of  Mackerel  Cove  has 
already  been  described.  Farther  eastward,  also  north  of  the  granite, 
occurs  a  pre-Carboniferous  greenish  rock,  here  called  the  Diunpling  rock. 

LINE  OF   SEPARATION   BETWEEN   CARBONIFEROUS  AND  PRE-CARBONIFEROUS 

ROCKS. 

If  now  the  northern  line  of  outcrop  of  the  western  part  of  the  granite 
and  the  pre-Carboniferous  greenish  Dumpling  rock  farther  eastward  on 
Conanicut  be  connected  with  the  northern  exposures  of  the  green  shales  on 
Rose  Island,  the  most  northern  exposures  of  green  shales  on  Gull  Rock 
Island,  and  the  most  northern  of  the  green  shales  exposed  along  the  southern 
end  of  Coasters  Harbor  Island,  east  of  the  arkose  exposure,  then  it  will  be 
noticed  that  arkose  occurs  immediately  north  of  this  line  at  Mackerel  Cove, 
Conanicut,  on  the  southern  end  of  the  tongue  of  land  extending  north  from 
Rose  Island,  and  at  the  southwest  corner  of  the  tongue  of  land  at  the  south- 

'  Prof.  T.  Nelson  Dale  suggests  that  uncoil  form ities  betvreeu  tbe  Cambrian  and  Carboniferous  are 
quite  natural.  There  may  be  an  uuconforniity  here,  but  the  abrupt  linear  contact  between  the  arkose 
and  the  green  shale,  with  the  very  marked  variance  between  their  dips  and  strikes,  seems  to  exceed 
that  of  ordinary  uuconformities.  There  is  no  direct  evidence  that  the  Carboniferous  arkose  is  resting 
upon  the  eroded  surface  of  the  Cambrian  shale. 


GOAT  ISLAND  AND  LITTLE  LIME  ROCK.  309 

ern  end  of  Coasters  Harbor  Island.  The  arkose  is  of  Carboniferous  age. 
The  greenish  rocks  south  of  this  hne  are  supposed  to  be  of  pre-Carbon- 
iferous  age. 

In  the  hght  of  this  interpretation  attention  may  be  called  to  the  facts 
that  a  north-south  line  along  the  middle  of  Mackerel  Cove  probably 
separates  the  pre-Carboniferous  granite  from  the.  Carboniferous  Conani- 
cut  shales  on  the  westward,  and  also  that  a  line  extending  along  the 
western  margin  of  the  land,  just  offshore  from  Coasters  Harbor  Island,  to 
the  end  of  Long  Wharf,  and  thence  more  east  of  south,  east  of  the  Spindle 
or  Little  Lime  Rock  to  the  southeast  corner  of  Newport  Harbor,  then 
southeast,  east  of  the  granite  exposures  in  Morton  Park,  south  of  Newport, 
and  along  the  middle  of  Almys  Pond,  represents  the  dividing  line  between 
the  pre-Carboniferous  rocks  on  the  west  and  the  Carboniferous  series  on 
the  east  of  this  line.  Thence  the  line  extends  eastward  north  of  Sheep 
Point.     All  of  these  lines  are  believed  to  be  due  to  faulting. 

GOAT  ISLAND  AND  LITTLE  LIME  ROCK. 

The  pre-Carboniferous  green  shales^  have  been  reached  in  deep  wells 
on  Goat  Island,  and  they  occur  on  Spindle  or  Little  Lime  Rock,  and  they 
occur  again  as  a  series  of  rocks  following  each  other  in  a  north-south  direc- 
tion which  are  exposed  at  low  tide  sotitheast  of  Lime  Rock.  The  dip  and 
strike  of  these  exposures  were  not  carefully  investigated,  there  being  no 
means  at  hand  of  distinguishing  cleavage  from  real  stratification. 

FORT  GREENE. 

South  of  Fort  Greene  Park  carbonaceous  black  shales  are  well  exposed 
along  the  shore.  They  are  banded  here  with  thin  layers  of  a  whiter, 
sandy  rock,  recalling  the  thicker  interbedded  white  rock  on  Bishop  Rock 
and  on  the  west  side  of  Coddington  Neck.  Thin  seams  of  coal,  or  at  least 
of  very  coaly  shale,  are  said  to  have  been  struck  at  various  times  in  the 
cemetery  a  quarter  of  a  mile  east  of  Fort  Greene  Park. 

MORTON   PARK  AND   SOUTHWARD. 

Granite  is  well  exposed  in  the  western  half  of  Morton  Park.  Toward 
the  southeastern  end  of  the  grounds  sandstone  and  blue-black  slialy  rock 
are  seen  striking  east  of  north  and  dipping  steeply  westward.     A  better  set 

'  The  author  does  not  distingtiish  between  shales  and  slates  or  phyllites  in  this  part  of  the  report. 


310  GEOLOGY  OF  THE  NARRAGANSETT  BASIN. 

of  exposures  occurs  half  a  mile  southward,  east  of  Almys  Pond.  Here 
sandstone,  shaly  sandstone,  and  conglomerate  are  interbedded.  The  con- 
glomerate contains  medium-sized  pebbles  of  a  quartzitic  rock.  Here  also 
the  strike  is  a  little  east  of  north  and  the  dip  very  steep  westward. 

NORTHEAST  LINES   OF  POSSIBLE  FAULTING. 

It  may  be  noticed  that  a  line  connecting  the  most  northern  exposure 
of  the  greenish  Sheep  Point  rock,  along  the  eastern  end  of  Bailey  Beach,  with 
its  most  northern  exposure  on  the  east  side  of  Newport,  north  of  Sheep 
Point,  takes  a  northeast  direction,  and  north  of  this  line  lie  the  Carbonifer- 
ous rocks  of  the  Newport  Cliffs,  evidently  faulted  against  the  older 
series.  Moreover,  along  the  northeasterly  trend  of  the  coast  forming  the 
southern  border  of  Newport  Harbor,  the  pre-Carboniferous  green  shale 
series,  elsewhere  called  the  pre-Carboniferous  green  shale  of  Newport  Neck, 
occurs  at  several  localities.  Little  Lime  Rock  and  the  series  of  green  shales 
southeast  of  that  locality  have  already  been  mentioned.  Lime  Rock  itself 
belongs  to  this  shale  series,  although  itself  composed  of  limestone. 

The  promontory  a  quarter  of  a  mile  southwest  of  Lime  Rock,  con- 
sisting of  green  shale  and  limestone,  and  the  similar  exposure  northeast  of 
the  stables  on  the  southwest  side  of  Brentons  Cove  belong  to  the  same 
shale  series. 

On  the  other  hand,  the  rocks  immediately  south  of  the  exposures  just 
mentioned,  which  form  the  neck  proper,  are  granite  eastward,  and  a  green- 
ish and  purplish  fine-grained  rock  of  uncertain  character,  looking  like 
argillite,  westward,  as  will  be  seen  from  the  map,  or  from  the  description  of 
the  rocks  forming  the  neck. 

CARBO]^fIFEROUS   KOCKS  ALOIffG  THE  NEAVPORT  CLIFFS. 

The  discussion  of  the  series  of  rocks  forming  the  cliffs  at  Newport  has 
been  left  to  the  last,  since  least  is  known  about  them.  It  was  intended  to 
prepare  a  careful  detailed  section  of  these  beds,  but  considering  the  small 
amount  of  time  at  the  writer's  disposal  and  the  inaccessibility  of  these 
rocks  except  at  low  tide,  it  was  decided  that  the  time  required  could  be 
more  profitably  employed  elsewhere.  This  was  especially  the  case  since 
the  cliff  exposures  could  not  be  definitely  brought  into  relation  with  others 
of  known  stratigraphic  position. 


NEWPORT  CLIFFS.  311 

The  section  along  the  chffs  at  Newport,  from  Easton's  Beach  to  the 
Forty  Steps,  mclucles  about  175  feet  of  rock,  the  strike  being,  in  general, 
north-south,  and  the  dip  variable  westward,  but  averaging  45°  W.  The  fol- 
lowino-  notes  will  give  an  idea  of  the  section  disclosed:  Southward  from 
Eastons  Beach,  going  upward  in  the  section,  3  feet  of  coaly  shale,  29  feet 
of  sandstone  with  shaly  layers,  dip  20°  W.;  4  feet  of  conglomerate  with 
pebbles  up  to  4  inches,  dip  45°  W.,  and  32  feet  of  sandstone.  Thence, 
going  down  in  the  series,  the  conglomerate  and  the  sandstone,  containing 
some  conglomerate  layers,  and  dipping  50°  W.,  are  passed  again.  Beneath 
occur  19  feet  of  coaly  black  shale,  containing  impressions  of  fern  leaves, 
15  feet  of  conglomerate  with  pebbles  up  to  4  inches  in  diameter,  22  feet  of 
sandstone,  and  an  unknown  thickness  of  carbonaceous  shaly  sandstone, 
disappearing  seaward,  these  last  being  the  lowest  rocks  exposed  along  the 
cliff.  Southward,  in  ascending  order,  the  cliffs  expose  20  feet  of  con- 
glomerate and  23  feet  of  shaly  or  fine-grained  sandstone,  dipping  80°  W. 
Southward,  in  descending  order,  the  conglomerate  occurs  again.  Then  in 
ascending  order  are  found  again  the  coaly  shale  and  sandstone;  then  7  feet 
of  conglomerate,  11  feet  of  shaly  sandstone  and  coaly  shale,  11  feet  of 
cono-lomerate,  40  feet  of  carbonaceous  sandstone  and  coaly  shale,  8  feet 
of  conglomerate,  27  feet  of  dark  carbonaceous  shaly  sandstone,  and  high  in 
the  bank,  just  before  reaching  the  Forty  Steps,  and  again  on  the  south  side 
of  the  steps,  a  layer  of  conglomerate.  At  the  steps  the  dip  has  become 
very  low  eastward,  the  pitch  being  plainly  southward,  about  15°. 

The  total  thickness  of  Carboniferous  rocks  south  of  Forty  Steps  does 
not  exceed  225  feet. 

The  conglomerate  at  the  Forty  Steps  is  11  feet  thick.  Overlying  it 
are,  in  ascending  order:  11  feet  of  black  shale  and  gray  sandstone,  almost 
horizontal;  11  feet  of  conglomerate,  west  of  a  fault,  dip  40°  W.;  11  feet  of 
sandstone  and  shale,  5  feet  of  conglomerate,  dip  steep  west;  24  feet  of 
brownish  shaly  rock;  more  faulting;  9  feet  of  conglomerate,  some  of  the 
pebbles  being  a  foot  long;  more  faulting;  13  feet  of  coaly  shale,  having  a 
steep  west  dip. 

After  the  coarse  conglomerate  with  large  pebbles  comes  in,  a  short 
distance  south  of  the  Forty  Steps,  layers  of  very  coarse  conglomerate  are 
seen  all  along  the  shore  as  far  as  Oclu-e  Point.  It  is  probable  that  a  care- 
ful study  of  the  section  along  this  part  of  the  coast  would  show  that  there 


312  GEOLOGY  OF  THE  NAERAGANSETT  BASIN. 

are  only  a  few  layers  of  very  coarse  conglomerate  present,  but  that  these 
extend  for  a  long  distance  along  the  shore,  their  continuit}'  being  inter- 
rupted by  small  faults.  A  detailed  description  of  the  southern  part  of  this 
section,  containing  the  coarse  conglomerate  layers,  is  of  little  value  until 
the  effect  of  the  faulting  has  been  clearly  determined.  In  a.  general  way 
it  may  be  stated  that  the  lower  coarse  conglomerate  layers  alternate  with 
coaly  shale  and  sandstone  beds,  as  do  the  lower  conglomerate  layers 
containing  relatively  smaller  pebbles  north  of  the  Forty  Steps.  The 
upper  coarse  conglomerate  beds  are  associated  with  a  series  of  greenish  or 
brownish-green  sandstones  and  shales,  which  are  best  exposed  farther 
west  and  up  the  cliffs  in  the  recesses  of  the  shore  north  of  Ochre  Point. 

At  the  promontory  south  of  the  Forty  Steps  the  rocks  dip  low  east. 
In  the  recess  of  the  shore  southward  the  dip  is  40°  W.  At  the  next 
promontory  southward  the  dip  is  again  very  low  west,  and  in  the  recess 
southward  the  dip  is  steeper  west  again.  Southward  the  faults  become 
more  frequent  and  the  steep  western  dips  are  more  common. 

The  coarse  conglomerates  and  the  associated  greenish  shales  and  sand- 
stones which  occur  higher  in  the  series,  and  which  are  exposed  in  the 
recesses  of  the  shore  northeast  of  the  Cornelius  Vanderbilt  mansion,  are 
exposed  all  along  the  northern  shore  of  the  cove  west  of  Ochre  Point.  If 
the  rocks  be  here  carefully  examined  at  low  tide,  the  conglomerate  layers 
will  be  found  to  be  usually  not  thick,  but  they  can  at  times  be  followed  for 
considerable  distances  along  the  shore.  They  show  the  presence  of  vari- 
ous small  anticlines  and  synclines,  especially  near  Ochre  Point,  and  also 
east  of  an  observation  hoiise  upon  the  sea  wall  farther  westward.  The 
series  in  general,  however,  is  evidently  almost  horizontal  dipping  as  a 
whole  very  low  westward. 

Along  the  northern  side  of  this  cove  a  few  of  the  shale  layers  asso- 
ciated with  the  coarse  conglomerate  are  in  places  black  rather  than  green, 
especially  near  the  western  side  of  this  shore  of  the  cove. 

The  total  thickness  of  the  formation  south  of  the  Fort}^  Steps  does 
not  seem  to  exceed  225  feet,  due  allowance  being  made  for  faulting,  so  that 
the  total  section  of  the  chff  series  so  far  seems  to  be  about  400  feet.  The 
most  striking  geological  feature  of  the  series  is  the  southward  pitch  of  the 
folds.  This  is  often  very  low,  but  at  times  becomes  very  steep  southward, 
especially  at  the  Forty  Steps,  and  at  another  promontory  exposing  coaly 


GEOLOGICAL  POSITION  OF  NEWPORT  CLIFF  EOCKS.  313 

sandstone  and  shale  farther  southward,  where  the  ^^itch  must  be  at  least 
15°  S.  This  southward  pitch  is  again  well  seen  along  the  northern  margin 
of  the  cove,  west  of  Oclu"e  Point,  where,  however,  it  is  very  low  south.  It 
continues  to  be  shown  at  the  northwestern  angle  of  the  cove. 

The  southward  pitch  of  the  folded  series  last  described  would  certainly 
carry  it  beneath  the  black  coaly  shale  series  exposed  along  the  western 
side  of  the  cove  almost  as  far  south  as  Sheep  Point.  This  series  of  coaly 
shales  and  black  carbonaceous  sandstones  contains  abundant  fern  leaves. 
It  strikes  approximately  north-south  and  dips  steeply  westward,  but  near 
its  northern  end  it  looks  very  much  as  though  it  overlies  the  green 
coarse  conglomerate  series  forming  the  north  side  of  the  cove.  Arkose  is 
found  in  the  northwestern  angle  of  the  cove.  Its  association  with  coaly 
shale  recalls  similar  exposures  on  Sachuest  Neck.  There  may  be  faulting 
here. 

When  the  very  marked  southward  pitch  of  the  cliff  series  of  conglom- 
erates is  considered  in  connection  with  the  marked  southward  pitch  of  the 
Eastons  Point  anticline  and  the  similar  pitch  of  the  rocks  on  Miantonomy 
and  Beacon  hills,  it  seems  as  though  the  cliff  conglomerates  mig-ht  repre- 
sent a  southern  extension  of  the  coarse  conglomerates  of  the  last-named 
localities  and  a  westward  continuation  of  the  Purgatory  conglomerate. 
The  failure  of  the  coarse  conglomerate  to  crop  out  along  the  western  hill 
slopes  of  Newport  and  at  points  southeast  of  the  Miantonomy  exposures  is, 
however,  difficult  to  explain  if  this  be  the  structure.  The  conglomerate 
layers  in  the  sandstone  east  of  Almys  Pond  are  hardly  satisfactory  evidence 
of  the  former  continuity  of  the  coarse  conglomerates  between  Eastons 
Point,  the  Newport  Cliff's,  and  Miantonomy  Hill.  In  any  event  the  New- 
port Cliffs  would  represent  only  the  basal  part  of  the  coarse  conglomerate 
section.  The  Fort  Grreene  and  the  Newport  Cemetery  coslj  shales  seem  to 
belong  beneath  the  coarse  conglomerate  stratigraphically. 

Newport  itself  seems  to  be  underlain  by  strata  belonging  to  the  Aqtiid- 
neck  series  (see  footnote  on  page  372).  If  this  be  true  the  Newport  Cliffs 
may  represent  a  section  formed  by  the  sharp  synclinal  infolding  of  rocks 
along  the  trend  of  the  cliffs.  This  synclinal  structure  was  accompanied  by 
considerable  subsidiary  folding,  and  involved  the  lower  part  of  the  conglom- 
erate series.  A  similar  strong  axis  of  folding  seems  to  have  been  present 
off  the  western  side  of  Codding'ton  Point  and  Coasters   Harbor  Island. 


314  GEOLOGY  OF  THE  NARRAGANSETT  BASIN. 

Southward  it  seems  to  have  ended  in  a  fault,  and  both  systems  of  infolding 
seem  to  have  been  accompanied  by  much  subsidiarj-  folding  and  faulting. 
Fossil  ferns  are  found  in  the  carbonaceous  shales  north  of  Sheep  Point, 
especially  at  the  promontories  a  little  over  a  quarter  of  a  mile  north  of  that 
point.  Fossil  oboli  occur  in  pebbles  at  various  points  a  short  distance 
north  of  Ochre  Point. 

XBWPOKT  jV^ECK  AND   SOUTHEEX  CLIFF  ROCKS. 

GREENISH  ROCK   IN  THE  CLIFFS  SOUTHWEST  OF  SHEEP  POINT. 

From  the  western  side  of  the  cove  west  of  Ochre  Point,  along  the 
shore  almost  as  far  as  Sheep  Point,  extends  a  series  of  black  coaly  shales, 
having  a  general  strike  parallel  to  the  shore  and  dipping  westward  at  vari- 
ous angles  averaging  about  50°.  A  short  distance  north  of  Sheep  Point 
a  greenish  rock  occurs,  whose  nearest  outcrops  are  within  a  few  feet  of  the 
coaly  shale;  but  while  the  general  trend  of  the  black  shales  is  about  N.  20° 
E ,  the  hne  of  contact  between  the  shales  and  the  green  rock  runs  about 
N.  45°  E.,  as  near  as  can  be  determined,  and  nearest  the  line  of  contact  the 
shales  are  much  crumpled  and  the  green  rock  has  been  so  much  sheared 
that  it  slightly  resembles  a  shale.  At  the  southern  end  of  the  point  the 
shearing  has  ceased  and  the  rock  is  seen  to  be  in  reality  massive.  Several 
hundi-ed  feet  south  of  Sheep  Point,  at  one  of  the  projecting  angles  of  the 
shore,  the  greenish  rock  has  included  a  rather  large  mass  of  a  rock  which  is 
bluish  and  very  fine  grained  when  fractured,  but  which  has  a  whiter  and  a 
more  stratified  appearance  where  subjected  to  weathering.  Macroscopically 
it  therefore  has  the  appearance  of  a  stratified  rock  much  contorted  and  cleft, 
the  crevices  being  penetrated  by  the  greenish  rock.  Fragments  of  a  similar 
rock  occur  farther  southward  and  present  at  times  an  appearance  very  much 
like  that  of  a  stratified  rock.  Their  nature  can  be  determined  only  by  micro- 
scopic examination.  Dikes  of  a  whitish  or  faintly  pinkish  aplite  are  also  not 
uncommon,  althougli  occurring  more  commonly  in  the  granite  area  farther 
southward.  In  places  the  greenish  rock  presents  the  appearance  of  flow 
structure.  About  three-eighths  of  a  mile  south  of  Sheep  Point  the  greenish 
rock  is  abruptly  terminated  by  contact  with  a  coarse-grained  granite  with 
large  phenocrysts  of  feldspar.  The  greenish  rock  here  has  a  more  evident 
granular  structure  than  usual  and  has  the  appearance  of  having  once  con- 


GRANITE  OF  jSTEWPOET  CLIFFS.  315 

tained  numerous  cavities  toward  the  contact,  the  cavities  having  later  been 
filled  with  a  greenish  mineral.  This  occurrence  of  apparently  amygdalar 
structure  is  itself  suggestive  of  the  igneous  origin  of  the  greenish  rock. 
But  it  may  result  from  replacement  of  contact  minerals  originally  due  to 
the  intrusion  of  the  great  granite  mass  into  the  greenish  rock. 

GRANITE  AREA  AT  THE  SOUTH  END  OF  THE  CLIFFS. 

The  granite  nearer  low-tide  mark  is  in  actual  contact  with  the  greenish 
rock,  maintaining  its  coarse  grain  and  the  large  size  of  its  phenocrysts  to 
the  contact.  Farther  from  low  tide,  somewhat  nearer  the  cliff  walk,  a 
band  of  the  pinkish  fine-grained  aplitic  rock  already  mentioned  intervenes, 
the  granite  terminating  abruptly  against  this  rock,  preserving  the  coarseness 
of  its  grain  and  the  large  phenocrysts  as  far  as  the  actual  contact  with  the 
pink  aplite.  The  pink  aplite  at  this  point  begins  with  a  much  finer 
grain,  and  preserves  this  to  its  actual  contact  with  the  green  rock.  The 
width  of  this  band  of  pink  aplite  is  6  to  8  inches.  Toward  the  sea  it 
partly  includes  fragments  of  the  greenish  rock  between  its  mass  and  the 
granite.  Nearer  shore  it  enters  the  granite  mass  at  one  point  with  a  less 
sharp  contact,  allowing  the  granite  to  come  in  contact  with  the  green  rock. 
The  pinkish  aplite  penetrates  the  greenish  rock  in  dikes  along  the  shore, 
one  of  these  dikes  being  much  coarser  in  grain  and  showing  more  granitic 
character,  ha^dng  apparently  possessed  both  macroscopic  feldspar  and  horn- 
blende, but  no  phenocrysts,  and  not  attaining  the  coarseness  of  grain  of  the 
main  granite  mass.  Some  of  these  facts  suggest  that  the  granite  is  more 
recent  than  the  greenish  rock.  Nothing  definite  can  be  stated.  In  many 
places  the  granite  is  itself  frequently  cut  by  the  pinkish  aplite.  The 
most  northern  exposure  of  the  granite  on  the  east  shore  is  a  little  north  of 
the  great  bend  where  the  southerly  trend  of  the  shore  from  Sheep  Point 
changes  to  the  more  rugged  southwestern  trend  of  the  shore  toward  Cog- 
geshalls  Point.  Thence  it  occupies  the  entire  line  of  the  shore  as  far  as 
Baileys  Beach,  south  of  Almys  Pond. 

A  greenish  rock,  appearing  like  a  dike,  occurs  in  the  most  northern 
exposure  of  the  granite  just  before  reaching  the  beach.  Another  greenish 
rock,  parallel  to  this,  contains  brecciated  fragments — probably  of  the 
same  general  mass,  but  looking  whiter  in  consequence  of  weathering — 
and  also  one  pebble  of  undoubted  quartzite.     At  the  eastern  end  of  the 


316  GEOLOGY  OF  THE  IS^ARKAGANSETT  BASlIy\ 

beach  there  occurs  an  additional  jnass  of  the  greenish  igneous  rock,  trav- 
ersed in  all  directions  by  whitish  streaks.  This  is  probably  a  continuation 
of  the  greenish  rock  from  the  eastern  shore,  near  Sheep  Point. 

GRANITE  AREA  ON   EASTERN   NEWPORT  NECK. 

At  the  western  end  of  the  beach,  south  of  Almys  Pond,  is  found  a 
reddish  granite,  to  a  certain  extent  resembling  the  groundmass  of  the  por- 
phyritic  granite  already  described,  but  lacking  phenocrysts.  Toward  Lily 
Pond  the  granite  has  changed  from  bright  red  to  a  much  darker  red,  due  to 
the  presence  of  an  abundance  of  some  darker  mineral.  These  granites  are 
frequently  cut  by  the  pinkish  fine-grained  aplite,  whose  character  as  a  dike 
rock  is  unquestionable  in  all  of  the  more  western  exposures.  This  second 
granite  area  includes  all  of  the  rock  between  Almy's  and  Lily  ponds,  the 
hill  immediately  west  of  Lily  Pond,  and  tlience  northward  as  far  as  the 
southern  margin  of  the  harbor  at  Newport,  excepting  perhaps  a  narrow 
border  along  the  shore,  which  seems  to  be  made  up  of  greenish  shales  similar 
to  those  found  elsewhere  about  the  harbor.  It  occurs  also  as  a  medium- 
coarse  granite  north  of  Almys  Pond,  in  the  western  part  of  Morton  Park. 

GREENISH   AND   PURPLISH  ARGILLITIC  ROCK  OF  MIDDLE   NEWPORT  NECK. 

West  of  the  granite  area,  as  far  as  Brentons  Cove,  the  western  side  of 
Rocky  Farm,  and  Prices  Neck,  occurs  a  fine-grained  rock,  varying  in  color 
from  green  to  dark  purjjle,  in  places  epidotic,  which  has  usually  been  called 
an  argillite.  It  contains  traces  of  banding  very  similar  to  stratification,  but 
which  might  be  interpreted  as  flow  structure.  In  the  northwestern  part  of 
this  area  Prof  T.  Nelson  Dale  found  a  fragment  of  undoubted  quartz- 
porphyry  embedded  apparently  in  a  cement  composed  of  clastic  material. 
This  would  indicate  that  at  least  a  part  of  the  area  was  of  sedimentary 
origin.  This  rock  is  closely  related  to  the  Dumpling  Rock  and  the  greenish 
rock  southwest  of  Sheep  Point. 

PRE-CARBONIFEROUS   GREEN    AND    PURPLE    SHALES    OF   WESTERN    NEWPORT 

NECK. 

The  western  part  of  Newport  Neck,  including  all  the  area  west  of  a 
line  drawn  through  the  marshes  from  the  western  side  of  Prices  Neck  to 
the  southern  end   of  Brentons   Cove,  is   occupied  bj^   a  series   of  shales. 


WESTERN  END  OF  NEWPORT  NECK.  317 

Their  usual  color  is  greenish,  and  very  frequently  whitish;  more  sandy,  thin 
layers  are  interbedded,  giving  the  rock  a  banded  appearance.  This  banded 
character  is  well  seen  at  various  points  on  the  east  side  of  Brentons  Point. 
Sometimes  the  rock  is  rather  quartzitic  and  is  cleaved  like  the  rock  on  the 
hill  east  of  Browns  Point,  east  of  Sakonnet  River;  one  locality  of  this 
kind  is  found  along  the  east  side  of  the  road  leading  northward-  into  the 
Fort  Adams  grounds  and  southwest  of  Brentons  Cove.  Not  infrequently 
the  shales  are  purphsh  in  color,  and  where  this  is  the  case  thin  layers  of 
limestone  are  often  intercalated  in  the  shales.  The  same  feature  was  noted 
in  the  Little  Compton  shales,  and  suggests  the  identity  of  these  shales. 
Calcitic  layers  not  being  known  from  undoubted  Carboniferous  rocks,  nor 
having  been  found  elsewhere  in  the  field,  suggests  that  the  Brenton  Point 
shales  are  of  pre-Carboniferous  age. 

Layers  of  calcite  are  especially  numerous  around  the  vicinity  of  Pirates 
Cave  and  the  shore  just  south  of  the  irregular  headland  a  quarter  of  a  mile 
southeast  of  Castle  Hill.  Along  the  summit  of  Castle  Hill  some  masses  of 
limestone  occur,  but  it  is  not  certain  whether  the  material  is  in  situ.  Around 
Brentons  Cove,  however,  these  interbedded  calcitic  layers  are  thicker  and 
apparently  more  common. 

The  average  strike  of  the  above-described  shales  is  N.-S.,  and  the  dip 
30°  to  40°  E.  However,  on  the  southern  and  western  shores  of  Brentons 
Point  the  strike  is  frequently  N.  30°  W.,  varying  at  times  to  N.  70°  W., 
and  the  dip  occasionally  becomes  almost  horizontal,  and  near  the  southwest 
end  of  Brentons  Point  and  north  of  Pirates  Cave  becomes  locally  even 
westward.  The  most  northern  exposure  of  the  green  shales  on  the  neck 
is  south  of  the  wharves  on  the  east  side  of  Fort  Adams.  A  sixth  of  a 
mile  south  of  the  wharves,  at  a  prominent  angle  of  the  shore,  the  green 
shale  contains  thick  limestone  layers. 

The  existence  of  these  limestone  beds  in  tlie  green  shale  series  is  of 
importance,  since  nothing  similar  occurs  in  the  undoubted  Carboniferous 
rocks.  A  hmestone  bed  is  found  northeast  of  the  stables  on  the  prominent 
angle  of  the  shore  at  the  southwest  side  of  Brentons  Cove.  It  strikes  about 
N.  10°  E.  and  dips  steeply  eastward.  A  quarter  of  a  mile  northward,  near 
Fort  Adams,  the  hmestone  occurs  again,  as  already  mentioned.  Here  it  is 
much  crumpled,  but  seems  in  general  to  strike  N.  70°  E.,  dip  southward. 


318  GEOLOGY  OF  THE  NARRAGANSETT  BASIN. 

A  much  thicker  bed  forms  the  two  exposm-es  at  the  Lime  Rock  hght-house, 
whose  strike  seems  to  be  approximately  east-west,  dip  steep  southward. 
A  bed  of  hmestone  more  nearly  agreeing  in  thickness  with  the  two  occur- 
rences above  described  is  found  on  the  promontory  a  quarter  of  a  mile 
southwest  of  Lime  Rock.  Here  again  it  is  prominently  associated  with  the 
green  shale  series,  and  strikes  N.  50°  to  60°  E.  and  dips  steeply  northward. 
Limestone  beds  are  also  said  to  have  been  struck  in  penetrating  the  green 
shales  which  underlie  Goat  Island.  These  thicker  calcite  beds,  which  occur 
along  the  southern  border  of  Newport  Harbor,  are  in  places  coarsely 
crystalline  in  consequence  of  metamorphism,  but  usually  show  a  fine  grain, 
and,  though  white  within,  weather  to  a  peculiar  light-brown  color.  The 
thinner  beds  of  calcite,  however,  south  of  Pirates  Cave  and  in  the  Little 
Compton  shales  are  usually  tinted  with  pink  or  reddish  purple. 

So  far,  in  all  eastern  Massachusetts  and  Rhode  Island,  only  two  forma- 
tions of  Paleozoic  age  have  been  discovered,  the  Cambrian  and  the  Car- 
boniferous. The  Carboniferous  is  nowhere  known  to  contain  true  limestone 
beds  of  sedimentary  origin.^  The  Olenellus  Cambrian  at  almost  all  of  the 
localities  where  it  is  known  to  occur  in  these  States  contains  limestone  inter- 
bedded  with  shales,  resembling  especially  the  thinner  limestone  beds  of  the 
green  and  purple  shale  series  in  the  southern  Narragansett  Bay  region.  In 
view  of  these  facts  search  for  fossils  was  made  in  these  southern  localities, 
but  without  success.  The  determination  of  the  age  of  these  shales  as  pre- 
Carboniferous  therefore  rests  upon  two  facts — the  presence  of  limestone 
layers  and  the  entire  absence  of  carbonaceous  material  in  any  of  these  beds. 

If,  in  addition,  the  relations  of  the  arkose  to  the  green  shale  series  at 
Sachuest  Neck  be  taken  into  account,  and  the  occurrence  of  the  arkoses  at 
the  line  of  contact  between  the  green  shale  series  of  supposed  pre-Car- 
boniferous  age  and  the  Carboniferous  rocks  on  Conanicut,  Rose  Island,  and 
Coasters  Harbor  Island  be  considered,  an  assumption  of  the  pre-Carbonif- 
erous  character  of  the  green  shale  series  affords  a  more  ready  explanation  of 
the  cause  of  its  present  distribution,  faults  having  thrown  pre-Carboniferous 
rocks  upward  on  the  south  side  of  the  faults,  against  higher-lying  Carbonif- 
erous rocks. 

'  As  will  be  seen  from  Mr.  Woodworth's  part  of  this  monograph,  there  are  limestone  deposits  in 
the  Wamsutta  series,  but  these  are  probably  of  secondary  origin,  owing  their  formation  to  the  injec- 
tion of  igneous  rooks  in  the  area  in  which  they  are  found. — N.  S.  S. 


CODDINGTON  COVE  TO  LAWTONS  VALLEY.  319 

SHALE  SERIES  FROM  CODDINGTON  COVE  TO  LAWTOKS  VALLEY. 

In  the  railway  cut  southeast  of  Coddington  Cove  the  bluish-black  shale 
is  exposed  for  a  quarter  of  a  mile.  The  cleavage  dips  15°  to  20°  W. 
In  the  most  eastern  part  of  the  indentation  at  Coddington  Cove  black  shale 
is  exposed  again,  the  cleavage  dipping  10°  to  20°  E.  Three-quarters  of  a 
mile  northward,  south  of  the  angle  of  the  shore  directly  east  of  Gould 
Island  light-house,  the  dark  carbonaceous,  often  black,  shale  is  seen  in  the 
bank.  It  is  much  cleaved,  the  dip  of  the  cleavage  being  low  eastward. 
Northward,  in  the  concave  curve  of  the  shore,  gray-blue  sandstone  is 
interbedded  with  the  coaly  shale.  The  cleavage  still  dips  only  5°  to  10° 
E.,  but  the  real  stratification  shows  strike  N.  21°  E.,  dip  25°  to  30°  E.  At 
the  north  end  of  this  cove  the  most  western  part  of  the  shore  line  shows 
more  of  the  carbonaceous  sandstone  interbedded  with  coaly  shale;  strike 
N.  12°  W.,  dip  about  60°  E.  A  few  fern-leaf  impressions  occur  in  the 
shale  here.  Over  the  sandstone  lies  more  of  the  coaly  shale.  The  sand- 
stone and  shale  continue  to  be  exposed  for  half  a  mile  northward,  the  strike 
changing  at  the  north  end  to  N.-S.,  dip  50°  E.  The  cleavage  is  low 
west.  Along  the  railroad  southward,  near  the  north  end  of  the  cut,  greenish 
shale  and  sandstone  occur,  the  latter  including  thin  layers  of  fine  conglom- 
erate. These  greenish  rocks  evidently  belong  in  the  blue  shale  series, 
but  overlie  the  shore  exposures.  Along  the  east- west  road  northward, 
nearly  half  a  mile  from  shore,  black  shale  is  exposed.  Where  the  next 
creek  northward  crosses  the  road  from  Newport  to  Bristol  Ferry,  the 
greenish-blue  shale  series  is  exposed  in  the  creek  bed  west  of  the  road.  A 
little  south  of  the  mouth  of  this  creek  coaly  shale  and  sandstone  are  found 
in  numerous  fragments  in  the  banks,  as  though  occurring  in  situ  farther 
back  from  the  face. 

East  of  Carrs  Point  and  south  of  Lawtons  Valley  the  north  end  of 
the  railway  cut  shows  coaly  shale  and  carbonaceous  sandstone;  strike 
N.  15°  E.,  dip  15°  E.,  as  far  as  could  be  determined;  the  exposure  is  not 
satisfactory.  The  blue  shale  series  is  exposed  along  Lawtons  Valley, 
about  half  a  mile  south  of  the  point  where  this  valley  crosses  the  Newport 
raod,  and  where  the  east-west  road  leaves  the  Newport  road  eastward 
for  the  Glen  region  on  the  east  side  of  Aquidneck.  Up  the  road  eastward 
the  blue-black  shales  are  exposed  as  far  as  the  brow  of  the  hill.     A  little 


320  GEOLOGY  OF  THE  NAREAGANSETT  BASIN. 

nortliward  from  this  road,  along-  the  Newport  road,  the  bkie-black '  shale 
fragments,  apparently  almost  in  sitn,  show  freqnent  fern-leaf  impressions. 
Farther  northward,  in  the  roadside,  greenish  shale  occurs.  These  green 
shales  are  seen  again  east  of  the  road  on  the  northwestern  side  and  along 
the  summit  of  tlie  hill,  and  are  overlain  on  the  eastern  side  of  the  hill  by 
fine-grained  grayish-green  sandstone  striking  about  N.-S.  and  dipping  30° 
to  40"  E.  This  sandstone  is  exposed  again  northward  along  the  strike  on 
the  west  side  of  the  road.  This  exposure  serves  to  confirm  the  exadence 
of  the  general  eastward  dip  of  the  rocks  along  the  western  side  of  the 
island,  a  feature  so  much  better  shown  to  the  northward.  The  dark  green- 
ish-blue shales  are  also  well  exposed  where  Lawtons  Valley  crosses  the 
east-west  road  leading  toward  the  Glen. 

GREEXISH-BIjUE  SHAIjES  of  SLATE  HILL  AND  SOUTIIAVARD. 

Along  the  East  Newport  road,  east  of  the  highest  part  of  Slate  Hill, 
bluish  shale  tinged  with  green  is  exposed  west  of  the  road.  A  quarter  of 
a  mile  southward  the  shale,  here  colored  dark  blue,  at  one  point  verging 
to  black,  occurs  interstratified  with  sandstone.  The  strike  is  N.  15°  E.,  dip 
apparently  low  E.,  about  10°.  Half  a  mile  southwest  along  the  road, 
where  it  begins  to  descend  the  hill  more  rapidly,  the  greenish-blue  shale  is 
exposed,  and  tlii-ee-eighths  of  a  mile  farther  on  it  is  seen  for  the  last  time 
on  the  west  side  of  the  road.  The  isolated  conglomerate  exposm-e  thi-ee- 
quarters  of  a  mile  farther  southwest  has  already  been  mentioned. 

SHALE  SERIES  NORTH  OF  LAWTONS  VALLEY. 

SHORE   EXPOSURES   NORTH   OF  COGGESHALL   POINT. 

Coaly  shale  is  exposed  along  the  shore  tlii-ee-quarters  of  a  mile  north 
of  Portsmouth  Grove  Station  and  continues  northward.  Near  Corys  Lane 
fine-grained  sandstone  overlies  the  shale  and  contains  plant  impressions. 
North  of  Corys  Lane  the  shore  offers  material  for  a  detailed  partial  section 
as  follows,  in  descending  order,  going  northward : 

Section  north  of  Corys  Lane. 

Feet. 

Fine  sandstone 13 

Black  coaly  shale,  containing  Sphenophyllum  equisetiformis,  Annularia  longifolia, 

and  large  fern- frond  impressions 9 

Sandstones,  in  j)laces  somewhat  coarse 7 


PORTSMOUTH  MINE,  321 

Section  north  of  Corys  Lane — Continued. 

Feet- 

Black  coaly  shale 4= 

Sandstone ■ 10 

Coaly  bed,  with  low  eastward  dip 20 

Black  coaly  shale 4 

Black  shale  and  very  tine-grained  sandstone,  Tfith  low  eastward  dip  (about  10°), 

showing  abundant  traces  of  plant  remains 9 

Fine-grained  sandstone 4 

Coaly  shale  and  fine-grained  sandy  rock,  striking  about  parallel  to  the  shore  and 

dipping  20°  B 8 

Coaly  shale 17 

Black  shale,  dipping  10°  to  15°  E 15 

Not  exposed 5 

Shaly  sandy  rock 1 

Coaly  shale 9 

The  section  terminates  a  little  over  half  a  mile  south  of  Portsmouth 
Mine  Station,  south  of  the  mouth  of  the  creek. 

PORTSMOUTH    MINE    AND    NORTHEASTWARD. 

At  the  Portsmouth  mine  (see  footnote  on  page  381)  three  beds  of 
coal  were  formerly  mined.  The  dip  was  about  35°  SE.,  the  strike  having 
changed  here  considerably  toward  the  east.  The  old  dump  shows  coal, 
black  shaly  slate,  and  black  sandstone,  sheared  until  a  part  of  this  is  also 
schistose.  Calamites,  Anmdaria  longifolia,  and  many  fern-leaf  impressions 
occur  here. 

Three-quarters  of  a  mile  northeastward,  on  the  hillside  east  of  the 
railroad,  a  coal  seam  was  also  once  opened,  and  the  dump  shows  the  same 
kind  of  rocks  as  at  the  Portsmouth  mine. 

A  quarter  of  a  mile  south  of  the  Bristol  Ferry  hotel  the  roadside  shows 
coaly  shale,  striking  apparently  N.  35°  E.,  dip  50°  E.;  not  satisfactory. 

A  little  south  of  the  last  exposure  a  road  turns  off  eastward,  toward 
the  south  end  of  Town  Pond.  Here  carbonaceous  sandstone,  some  of  the 
layers  coarse,  contains  fragments  of  carbonaceous  shale,  much  crumpled, 
apparently  by  a  force  acting  east-west. 

A  boring  in  Portsmouth,  Rhode  Island,  examined  by  Mr.  Collier  Cobb, 
gave  the  following  record  as  regards  succession  and  thickness,  but  no 
account  is  taken  of  possible  reduplication  by  faulting  or  folding.  In  this 
table  argillaceous  strata  in  superposition  and  variously  denominated  argil- 

MON  XXXIII 21 


322  GEOLOGY  OF  THE  NAEEAGANSETT  BASIN". 

lite,  slate,  and  shale  fire  clay  in  tlie  original  record  have  been  grouped 
together  as  a  single  bed  under  the  name  argillite: 

Record  of  boring  in  Portsmouth^  Rhode  Island. 

Feet.  Inches. 

1.  Below  casing,  fire  clay 13          1 

2.  Argillite,  dark  colored,  growing  lighter  aud  becomiug  friable  downward .  9          4 

3.  Argillite,  in  upjier  part  slaty,  banded  and  light  gray,  crossed  by  seams 

of  epidote  and  magnetite 8          7 

4.  Gray  sandstone 8 

5.  Drab  slate 1          0 

6.  Gray  sandstone,  containing  calcite 3        11 

7.  Brecciated  slate 1          0 

8.  Carbonaceous  argillite 2          1 

9.  Goal,  with  quartz  impurities,  brecciated 3          0 

10.  Carbonaceous  argillite 2          6 

11.  Coal,  some  quartz  in  uppermost  part 3          9 

12.  Slate 6 

13.  Goal,  considered  good  up  to  49  feet  10  inches 2          9 

14.  Quartz  aud  slate  breccia 2 

15.  Goal,  filled  with  fine  particles  of  calcite 3          0 

16.  Argillite   8          1 

17.  Argillaceous  slate 2          4 

IS.  Brecciated  carbonaceous  matter,  containing  quartz  and  some  magnetite .  4 

19.  Argillaceous  shale 2          2 

20.  Coal,  with  quartz  and  iron  pyrite 3 

21.  Argillaceous  shale 4          7 

22.  Highly  carbonaceous  shale 6          2 

23.  Quartz,  with  fire  clay 5          8 

24.  Fire  clay,  like  top  of  hole 1          3 

25.  Argillaceous  shale   2          8 

26.  Fine  sandstone  4 

27.  Quartz ;  probably  chlorite  gives  the  green  color  to  a  part  of  the  quartz.  3 

28.  Argillite,  dip  24° 5 

29.  Sandstone,  showing  feldspar  and  chloritic  development 6          0 

30.  Goal,  containing  magnetite 1 

31.  Quartz,  containing  chlorite  and  pyrite 1 

32.  Sandstone 9          3 

33.  Argillite,  brecciated 3          6 

34.  Sandstone 13          7 

35.  Quartz  vein 1 

36.  Sandstone,  discolored  by  iron  oxide,  with  quartz  veins,  feldspar,  and 

chlorite 16          5 

37.  Carbonaceous  shale 4          1 

38.  Slate,  drab  in  color,  with  iron  pyrite 4          6 

39.  Carbonaceous  shale,  with  quartz  veins 2 

40.  Black  shale,  with  small  quartz  veins  and  iron  pyrite 4          7 


EEGOED  OF  BOEING  IN  POETSMOUTH.  323 

Feet.  Inches. 

41.  Argillite 6 

42.  Sbale 7  0 

43.  Sbale,  black  and  carbonaceous,  contaius  some  quartz 2  0 

44.  Sandstone 4  8 

45.  Sandstone,  more  compact  and  modern  than  above 1  1 

46.  Sandstone 6 

47.  Sandstone 1  0 

48.  Slate,  with  crystals  of  iron  pyrite 3  0 

49.  Quartz  vein -_ -      1 

50.  Slate,  crossed  by  small  veins  of  quartz,  calcite,  and  iron  pyrite 9  4 

51.  Sandstone,  dark  and  tine  grained 4  11 

52.  Slate,  very  hard  and  fine  grained 8  6 

53.  Sandstone,  hard  and  fine  grained 1  3 

54.  Shale,  hard  and  black 7  4 

55.  Coal,  a  highly  carbonaceous  graphitic  bed 2  1 

56.  Slate,  hard - 7  11 

57.  Quartz  vein 1 

58.  Slate,  hard 3  8 

59.  Shale,  carbonaceous 5  8 

60.  Shale,  sandy 4  6 

01.  Slate,  hard  and  black,  carbonaceous 5 

62.  Slate,  hard,  black,  and  sandy 7  11 

63.  Slate,  hard  and  black , 

64.  Quartz  vein 1 

65.  Slate,  hard,  black,  and  carbonaceous 3  6 

66.  Coal,  full  of  quartz  impurities 2 

67.  Slate .  1  0 

68.  Sandstone,  fine  grained  and  hard 2  1 

69.  Quartz  vein    : . .  1 

70.  Sandstone,  fine  grained 4  0 

71.  Sandstone,  fine  grained 2  1 

72.  Shale,  hard,  passing  into  a  hard  fine-grained  sandstone 10  1 

73.  Shale,  carbonaceous 2  2 

74.  Shale,  arenaceous,  passing  into  a  fine  sandstone 3  0 

75.  Sandstone,  fine  grained 2  0 

76.  Shale,  carbonaceous 4  9 

77.  Shale,  fine  grained 1  2 

78.  Shale,  sandy 3  7 

79.  Sandstone,  gray,  hard,  and  fine 3  9 

80.  Shale,  black,  fine  grained 2 

81.  Shale,  arenaceous,  with  bands  of  graphite 3  7 

82.  Shale,  black 1  8 

83.  Sandstone,  fine  grained 2  3 

84.  Shale,  black,  with  quartz 2 

85.  Sandstone,  with  quartz  veins 3  3 

86.  Sandstone 6  0 


324  GEOLOGY  OF  THE  NAERAGANSETT  BASIN. 


87.  Graphite,  impure  1  6 

88.  Sandstone 2  10 

89.  Shale,  black  and  highly  carbonaceous 1  C 

90.  Coal li 

91.  Sandstone 3  9 

92.  Quartz  vein 3 

93.  Sandstone 1  4 

94.  Quartz  vein 1 

95.  Sandstone,  gray 3  9 

96.  Slate,  drab  arid  hard 2  3 

97.  Slate,  same  as  above 3  2 

98.  Sandstone 8 

99.  Shale,  carbonaceous 1  0 

100.  Sandstone,  fine  grained 1  4 

101.  Shale,  carbonaceous 4 

102.  Sandstone,  gray 10 

103.  Sandstone,  dark  gray '...  3 

104.  Sandstone,  lighter  gray 5  0 

105.  Sandstone,  dark  gray 1  4 

106.  Shale,  carbonaceous 9  8 

107.   3  1 

108.  Sandstone,  fine,  filled  with  carbonaceous  matter 1  6 

109.  Sandstone 1  8 

110.  Sandstoue,  coarser  than  above 1  3 

111.  Sandstone,  with  thin  seams  of  carbonaceous  matter 4  0 

112.  Shale,  black  and  carbonaceous,  dip  43° 1  9 

113.  Sandstone,  dark  gray 4 

114.  Shale,  arenaceous,  filled  with  carbonaceous  matter 2  0 

115.  Slate,  black 1  8 

116.  Sandstoue,  like  that  at  120  feet  down 8 

117.  Shale,  carbonaceous 1  10 

118.  Shale,  arenaceous,  with  carbonaceous  matter 1  2 

119.  Sandstone 4 

120.  Shale,  arenaceous,  with  thin  seams  of  carbonaceous  matter 6  4 

121.  Shale,  highly  carbonaceous 2  0 

122.  Sandstone,  hard  and  fine  grained 1  0 

123.  Argillite - 4  9 

124.  Sandstone 1  0 

125.  Argillite 10 

126.  Sandstone,  hard  and  tine,  with  small  calcite  veins 1  3 

127.  Argillite,  carbonaceous 2  0 

128.  Shale,  arenaceous,  containing,  from  one-eighth  to  one-fourth  inch  apart, 

very  thin  layers  of  granite 3  0 

129.  Sandstone,  gray 3  3 

130.  Coal,  filled  with  quartz,  iron  pyrite,  and  chlorite 1 


EBCOED  OF  BOEma  IN  POETSMOUTH.  325 

Feet.  Inches. 

131.  Argillite 1  5 

132.  Saudstoue,  with  calcite  veins  and  iron  pyrite 1  0 

133.  Shale,  carbonaceous 4  n 

134.  Sandstone,  tine  to  coarse  grained,  with  calcite  veins 3  9 

135.  Sandstone,  hard  and  darker  than  above 1  lo 

136.  Sandstone,  like  above,  with  carbonaceous  matter 3  5 

137.  Sandstone,  fine  grained,  gray,  entirely  free  from  carbonaceous  matter. .  G 

138.  Shale,  carbonaceous 22  C 

139.  Sandstone,  fine  grained 1  (i 

140.  Shale,  carbonaceous y 

141.  Sandstone,  fine  grained 1 

142.  Slate,  hard,  black,  becoming  carbonaceous  toward  end,  dip  28°  at  top. .  4  0 

143.  Sandstone,  bard,  flue  grained 1  1 

144.  Goal,  broken  and  filled  with  calcite  covered  with  iron  ijyrite,  dip  63°. .  5 

145.  Sandstone,  fine  grained 3  2 

146.  Shale,  carbonaceous 1  0 

147.  Sandstone,  fine  grained  and  indurated 10 

148.  Coal,  brecciated  and  filled  with  calcite 2 

149.  Shale,  hard  black 6 

150.  Argillite 8  4 

151.  Shale,  black,  becoming  carbonaceous  toward  middle  and  arenaceous  at 

the  bottom 7  4 

152.  Coal  (carbonaceous  breccia) 3 

153.  Sandstone 9 

154.  Sandstone,  with  small  veins  of  calcite 1  0 

155.  Shale,  carbonaceous 1 

156.  Shale,  arenaceous 1  0 

157.  Shale,  highly  carbonaceous,  dip  36° 2 

158.  Sandstone 1  3 

159.  Sandstone,  gray 1  3 

160.  Argillite 3  8 

161.  Shale,  carbonaceous - 1  4 

162.  Shale,  hard,  fine,  and  arenaceous 2  6 

163.  Shale,  arenaceous 11 

164.  Shale,  arenaceous  and  carbonaceous  between  440  and  442  feet  down 22  1 

165.  Shale,  carbonaceous 4  5 

166.  Coal,  with  veins  of  quartz  near  bottom 6  5 

167.  Sandstone,  gray 1  0 

168.  Shale,  carbonaceous 3  1 

169.  Sandstone,  gray 3  10 

170.  Sandstone,  dark  gray  and  fine  grained 2  3 

To  bottom  of  hole,  475  feet  11  inches,  reached  February  23,  1887,  at  5.30  p.  m. 


326  GEOLOGY  OF  THE  NAEEAGANSETT  BASIN. 

LINE    OF   EXPOSURES    THREE-EIGHTHS   OF  A  MILE    WEST    OF   THE    NEWPORT 

ROAD. 

Almost  half  a  mile  north  of  Lawtons  Valley  a  much  smaller  stream 
gully  is  seen  extending  down  the  hillside.  On  the  south  side,  near  the 
railroad,  carbonaceous  black  shale  containing  occasional  fern-leaf  impres- 
sions is  exposed.  The  dip  is  apparently  very  low  eastward.  Farther  up, 
the  shale  turns  to  bluish  black.  At  the  brow  of  the  hill,  south  of  the  gtilly, 
there  occurs  a  small  conglomeratic  layer.  Toward  the  top  of  the  gully 
sandy  layers  come  in. 

The  creek  entering  the  marshy  pond  south  of  Coggeshall  Pond  also 
shows  dark  blue-black  shales,  with  interbedded  sandy  layers,  in  the  banks 
south  of  the  valley  and  near  the  railroad.  The  dip  is  at  first  40°  E., 
but  becomes  steeper  eastward.  The  same  series  continues  to  be  exposed 
farther  up  along  the  valley,  the  strike  at  one  point  being  N.  30°  E.,  dip 
very  steep  east.  The  rock  contains  sandy  layers  and  in  places  also  becomes 
very  carbonaceous.  At  the  brow  of  the  hill  north  of  the  creek  a  coarse, 
thick,  whitish  sandstone  layer  shows  a  strike  of  N.  30°  E.,  the  dip  appar- 
ently 60°  E.  Southward  this  sandstone  terminates  siiddenly,  but  north- 
ward it  continues  for  a  long  distance.  To  the  eastward  the  shale  series 
overlies  this  sandstone  again.  The  sandstone  contains  in  places  a  few  small 
pebbles.     It  forms  only  a  layer  in  the  shale  series. 

The  coarse  sandstone  is  exposed  again  three-eighths  of  a  mile  east  of 
north  of  the  creek.  Here  again  a  few  pebbles  occur.  Strike  N.  12°  E., 
dip  E.  Northeast  of  this  locality  the  same  coarse  sandstone  is  overlain  by 
carbonaceous  shale;  strike  N.  20°  E.,  dip  40°  to  45°  E.  Southeastward, 
halfway  between  the  last  two  exposures  and  the  Newport  road,  bluish-dark 
shale  is  exposed  at  several  localities,  evidently  overlying  the  coarse  sand- 
stone, and  apparently  dipping  steep  to  the  east.  Northwest  of  the  last 
sandstone  outcrop  dark-bluish  shale  is  exposed.  It  belongs  beneath  the 
sandstone  bed,  but  contains  itself  more  sandy  layers,  and  the  dip  is 
eastward,  although  apparently  only  20°.  The  last  exposure  extends  as 
far  as  an  east-west  road  running  to  the  beach.  A  quarter  of  a  mile 
northward  a  projection  at  the  northwestern  angle  of  the  hill  shows  a  more 
greenish  shale;  strike  N.  16°  E.,  dip  60°  E.  Another  exposure  of  the 
shale  occurs  a  quarter  of  a  mile  northward,  south  of  the  brook.     The  shale, 


BUTTS  HILL.  327 

more  bluish  in  color,  is  seen  again  north  of  the  brook,  along  the  south  side 
of  an  east- west  road;  strike  N.  20°  E.,  dip  very  steep  eastward.  In  the  fields 
north  of  this  road  the  shale  continues  to  be  exposed,  and  just  before  reach- 
ing the  road  which  crosses  the  140-foot  hill  (see  map,  PI.  XXXI)  southwest 
of  a  house  the  bluish  shale  is  exposed,  and  contains  a  more  sandy  layer 
just  south  of  the  building;   dip  not  certain,  strike  apparently  N.  35°  E. 

SHALE  SERIES  AT  BUTTS  HILL. 

Three-quarters  of  a  mile  northeast  of  Butts  Hill,  along  the  eastern 
Newport  road,  cai'bonaceous  shale  with  fern  leaves  and  other  plant  remains 
occurs.  Strike  N.  6°  E.,  curving  to  N.  20°  W  at  the  north  end  of  the 
exposure;  dip  15°  to  20°  W.  Northeast  of  Butts  Hill,  along  the  same 
I'oad,  just  noi'th  of  Chas  C.  Hazard's  house,  a  coal  mine  was  formerly  worked. 
The  strike  of  the  beds  is  N.  15°  E.,  dip  15°  to  20°  W.  The  structure  of 
the  northern  third  of  Aquidneck  Island  is  evidently  that  of  a  syncline. 

All  around  the  top  of  Butts  Hill,  especially  in  the  neighborhood  of 
the  old  fort,  the  bluish-black  and  coaly  shale  is  frequently  exposed.  North 
of  the  old  fort  and  just  south  of  the  road  crossing  the  hill  is  an  old  quarry. 
Near  the  top  of  this  exposure  the  blackish  shale  contains  fern-leaf  impres- 
sions. The  dip  of  the  shale  is  low,  5°  to  10°  S.  In  places  there  is  evidence 
of  much  crumpling  here  by  a  force  acting  east  and  west,  and  the  result  is  a 
series  of  narrow  folds  trending  north-south  and  giving  rise  to  variable  east- 
west  dips,  generally  to  the  westward  along  the  east  side  of  the  hill.  Butts 
Hill  evidently  lies  in  the  trough  of  the  syncline. 

GREEN  SHALES  AND  CONGLOMERATES  OF  THE  NORTHERN  SYNCLINE. 

GREEN    SHALES   ALONG    THE    WESTERN   NE\A?PORT    ROAD. 

Half  a  mile  north  of  the  point  where  the  Newport  road  crosses  Lawton 
Valley  greenish-blue  and  bluish  shales  occur  along  the  road  and  imme- 
diately westward.  The  strike  is  about  N.  10°  E.,  dip  probably  20°  E.  A 
mile  northward,  on  the  east  side  of  the  road,  greenish-blue  slate  and  sand- 
stone strikes  N.-S.,  dip  20°  to  40°  E.,  as  well  as  could  be  determined.  A 
quarter  of  a  mile  northward,  at  an  angle  of  the  road,  more  greenish  shale 
occurs.  Three-eighths  of  a  mile  northward  the  green  shale  is  seen  exposed, 
east  of  the  road  corners,  on  the  south  side  of  the  road.     Green  shales  occur 


328  GEOLOGY  OF  THE  NARKAGANSETT  BASIN. 

also  oil  tne  southwest  and  northeast  sides  of  the  hill  immediately  northward, 
and  again,  for  the  last  time,  a  quarter  of  a  mile  northward,  west  of  the  road. 
The  green  shales  therefore  form  a  series  overlying  the  bluish-black 
shales,  although  evidently  a  part  of  the  same  and  representing  only  the 
upper  courses  of  the  series. 

PORTSMOUTH   CONGLOMERATES. 

A  road  leads  from  Portsmouth  Grove  Station  eastward  to  the  Newport 
road.  An  eightli  of  a  mile  southeast  of  the  road  corners  conglomerate 
with  quartzitic  pebbles  up  to  10  inches  in  diameter  is  found.  The  trend  of 
the  exposures  is  about  N.  10°  to  15°  E.,  but  the  strike  and  dip  could 
not  be  satisfactorily  determined.  Northward,  the  same  distance  northeast 
of  the  road  corners,  bluish  sandstone,  varying  to  green,  in  places  coarse, 
and  with  some  layers  of  fine  conglomerate,  is  seen.  The  trend  of  the 
exposures  is  N.  12°  E.  A  quarter  of  a  mile  northeast  of  the  crossroads 
the  greenish  slate  is  seen  on  the  hillside  nearer  the  Newport  road,  becom- 
ing moi'B  bluish  eastward  and  merging  into  a  more  sandy  rock  toward  the 
northeast,  where  it  is  more  nearly  in  line  with  the  pre\nous  exposure. 
Three-quarters  of  a  mile  from  the  crossroads,  along  the  top  of  the  hill, 
considerable  sandstone  occurs.  It  includes  a  narrow  greenish  shale  layer, 
and  at  the  southwest  end  a  few  thin  conglomeratic  beds,  with  pebbles  not 
exceeding  half  an  inch  in  diameter.  An  eighth  of  a  mile  northeastward, 
and  the  same  distance  from  the  next  east-west  road,  greenish-blQC  shale 
again  occurs  westward,  with  gray  sandstone  eastward.  A  few  layers 
are  coarse,  almost  conglomeratic.  North  of  the  east-west  road  loose 
pebbles,  similar  to  those  usually  found  in  conglomerates,  occur  with  con- 
siderable frequency  on  the  east  side  of  the  hill,  east  of  the  regular  green 
shale  exposures  of  the  hill.  Over  three-fourths  of  a  mile  northward,  an 
eighth  of  a  mile  northeast  of  the  crossroads,  begins  a  ridge  extending 
N.  80°  E.,  across  the  next  road  leading  northward.  This  ridge  is  formed  in 
the  main  of  conglomerate,  composed  of  quartzitic  pebbles  often  8  inches 
or  longer  in  diameter,  and  containing  fossil  oboli.  The  conglomerate 
strikes  N.  20°  E.;  the  dips  are  difficult  to  determine,  but  seem  to  be  in  some 
places  nearly  vertical,  in  others  less  steep.  A  greenish-blue  shale  bed  is 
apparently  interbedded  in  places.  This  ridge  of  conglomerate  lies  half  a 
mile  a  little  west  of  south  of  Butts  Hill,  and,  like  the  shales  of  that  hill,  is 


POSITION  OF  SLATE  HTLL  SHALES.  329 

believed  to  occupy  the  axis  of  the  synchne.  If  that  be  true,  the  following 
exposures  may  be  of  interest,  since  they  lie  east  of  the  sandstones  and 
conglomerates  which  are  nearer  the  western  Newport  road. 

A  number  of  exposures  of  coarse  quartzitic  conglomerate  lie  a 
quarter  of  a  mile  directly  south  of  the  ridge,  and  south  of  an  east-west 
road.     Their  strike  seems  to  be  north-south. 

Three-quarters  of  a  mile  southward,  in  the  Portsmouth  camp-meeting 
grounds,  coarse  conglomerate  is  exposed,  interbedded  with  sandstone.  Stiike 
N.  7°  W.,  dip  70°  W.  This  exposure  seems  to  lie  on  the  eastern  side  of  the 
syncline. 

Southward  no  inore  coarse  conglomerate  is  exposed.  The  next  exposure 
lies  a  mile  southward,  south  of  the  next  east-west  road,  on  the  west  side 
of  the  hill.  Near  the  base  of  the  hill  occurs  bluish-green  sandstone  with 
narrow  streaks  of  pebble  layers,  the  pebbles  being  of  very  small  size. 
Farther  east  bluish-green  shale  is  exposed  at  several  points.  This  shale 
resembles  the  greenish  shales  described  as  occurring  beneath  the  sandstones 
and  conglomerates  on  the  west  side  of  the  syncline.  Their  occurrence  in 
the  same  position  on  the  east  side  is  significant.  Strike  north-south,  dip  low 
westward. 

RELATIONS  TO  SLATE  HILL  SHALES. 

It  will  be  seen  that  the  structure  of  the  northern  tliird  of  Aquidneck 
Island  is  that  of  a  syncline,  the  great  mass  of  the  rocks  being  dark  carbona- 
ceous shales,  and  to  a  less  degree  sandstones.  Overlying  these,  near  the 
top,  is  a  thin  series  of  greenish  shales,  and  a  remnant  of  a  conglomerate 
series  overlying  the  green  shales  is  still  preserved  in  places  near  the 
middle  of  the  syncline.  A  little  over  two  miles  south  of  the  green  shales 
above  described,  from  the  east  and  west  sides  of  the  syncline,  the  green 
shales  of  Slate  Hill  begin.  The  synclinal  structure  is  no  longer  apparent 
so  far  southward.  Instead  of  the  single  syncline  of  the  northern  third  of 
Aquidneck  the  soLithern  third  shows  at  least  three  synclines — one  east  along 
the  Sakonnet  shore;  a  second,  the  southward-plunging  syncline  in  the 
Paradise  Rock  series  and  west  of  Eastous  Point;  a  third,  just  west  of 
Miantonomy  Hill  and  in  the  Coasters  Harbor  Island  region. 

Possibly  the  green  shales  near  the  top  of  Slate  Hill  represent  the 
place  where  the  marked  southward  pitch  of  these  more  southern  synclines 


330  GEOLOGY  OF  THE  NARRAGAlSrSETT  BASIN. 

begins.  It  is  in  the  latitude  of  the  Slate  Hill  sections,  and  thence  east- 
ward and  westward  to  the  shore  on  either  side  of  Aquidneck  Island,  that  it 
is  most  difficult  to  secure  evidence  of  marked  strikes  and  dips,  a  character 
often  attending  shaly  rocks  not  steeply  inclined,  since  the  cleavage  then 
most  readily  obscures  the  stratification,  not  departing  far  from  its  plane. 


CHAPTER   VII. 

THE  KINGSTOWN  SERIES. 

Unity  and  lithological  character  of  the  Kingstown  sandstone  series. At       tllG      preSOllt      StagB 

of  investigation  it  does  not  seem  feasible  to  separate  the  Carboniferous 
strata  lying  along  the  western  border  of  Narragansett  Bay,  between  East 
Greenwich  and  Narragansett  Pier,  into  divisions  of  geological  value.  No 
fossils  have  so  far  been  discovered  in  them.  Lithologically  they  consist  of 
frequent  alternations  of  the  following  rocks: 

First.  A  coarse  quartzitic  sandstone,  almost  an  arkose,  evidently  derived 
in  large  part  from  some  earlier  granite  area.  This  sandstone  frequently 
contains  flakes  of  white  mica,  or  of  biotite  and  some  other  dark  mineral. 
The  color  of  the  sandstone  in  general  is  white,  the  quartzitic  elements  very 
much  predominating. 

Second.  As  this  sandstone  becomes  coarser  it  contains,  at  first,  scattered 
quartzite  pebbles,  and  then  thin  layers  of  a  conglomeratic  nature,  merging 
into  triie  conglomerates  a  few  feet  in  thickness,  the  pebbles  of  which  usually 
consist  of  quartzite,  occasionally  of  granite,  and,  except  in  a  few  localities, 
do  not  exceed  an  inch  or  one  inch  and  a  half  in  diameter. 

Third.  As  this  sandstone  becomes  finer  it  also  turns  darker,  the  varia- 
tion in  color  being  usually  due  to  an  increase  in  the  amount  of  carbonaceous 
material.  In  some  of  the  more  northern  localities,  however,  the  coarser  and 
medium-grained  sandstones  are  of  a  bluish  color,  which  appears  to  be  due 
to  a  decrease  in  the  quantity  of  carbonaceous  matter,  making  more  evident 
the  dissemination  of  iron  in  some  form  throughout  the  rock.  The  blue 
color  is  usually,  in  the  case  of  the  less  carbonaceous  sandstones,  a  sign  of 
less  metamorphism.  During  metamorphism  the  feiTuginous  matter  seems  to 
have  collected  partly  in  the  form  of  magnetite  and  partly  as  a  constituent  of 
black  mica,  leaving-  the  general  mass  of  the  rock  whitish,  but  flecked  with 
black  specks. 

Fourth.  The  medium-grained  sandstones  merge  into  a  very  fine-grained 

331 


332  GEOLOGY  OF  THE  KARRAGANSETT  BASIif. 

and  always  very  dark  or  black  rock,  the  color  being  due  to  its  carbon- 
aceous character.  It  is  difficult  to  determine  whether  to  call  this  rock  a 
fine-grained  sandstone  or  a  gritty  shale,  since  it  is  sometimes  massive  and 
without  cleavage  and  sometimes  shaly. 

Fifth.  This  merges  into  shale,  the  structure  being  due  to  cleavage. 
The  micaceous  elements  of  the  sandstones  here  become  yerj  abundant- 
Sericite  is  a  common  constituent;  the  color  at  a  distance  often  appears  rather 
dark,  almost  black,  especially  where  moistened  by  water;  but  at  closer  range 
it  usually  shows  a  dark-blue  color,  the  dark  tint  being  evidently  due  to  the 
presence  of  ferruginous  and  carbonaceous  matter. 

Sixth.  Occasionally  the  dark-blue  shale  becomes  black,  contains  much 
carbonaceous  matter,  and  is  comparable  with  the  coaly  shales  of  the  less 
metamorphosed  part  of  the  basin. 

The  types  of  rocks  described  above  alternate  in  an  irregular  manner, 
making  it  imjDOSsible  at  the  present  to  treat  of  them  otherwise  than  as  a 
geological  unit.  From  Hazzard's  quarry,  a  mile  north  of  Sauuderstown,  to 
the  angle  of  the  shore  a  third  of  a  mile  south  of  Watsons  Pier,  the  expo- 
sures are  almost  continuous.  Here  it  is  seen  that  the  shales  are  an  important 
part  of  the  Carboniferous  section  on  the  western  side  of  the  bay,  forming 
from  a  third  to  a  half  of  the  total  thickness  of  the  rocks  exposed.  The  fine- 
grained sandstones  are  another  important  element.  The  coarse  sandstones, 
although  a  conspicuous  feature  farther  inland,  can  here  hardly  form  a  fourth 
of  the  total  section. 

Away  from  the  coast,  westward  and  northward,  the  exposures  consist 
chiefly  of  sandstone,  often  coarse  and  conglomeratic.  Finer  sandstones  also 
occur,  but  shales  are  rather  infrequent,  excepting  in  the  regions  (1)  imme- 
diately south  of  Wickford.  (2)  a  mile  south  of  Sandy  Point,  on  Potowomut 
Neck,  and  (3)  a  mile  and  a  half  directly  south  of  tlie  second  locality. 
This  diminution  in  the  relative  amount  of  shale  exposed  toward  the  west 
is  striking,  and  would  appear  to  indicate  a  corresponding  lithological 
distinction  between  the  shore  exposures  and  the  more  inland  part  of  the 
Carboniferous  series  toward  the  west  and  north  were  it  not  for  the  pi'ob- 
ability  that  the  more  isolated  iidand  exposures  represent  chiefly  the 
harder,  less  eroded,  and  therefore  at  present  more  elevated  beds  of  the 
Carboniferous  series,  while  the  softer  and  less  enduring  rocks,  including 
the  finer  sandstones  and  especially  the  shales,  exist  in  considerable  thickness 


KINGSTOWN^  SERIES  AT  THE  BONNET.  333 

in  any  fully  exposed  section,  but  suffered  more  from  weathering  and  now 
lie  hidden  nnder  the  more  recent  glacial  and  sand-plain  deposits,  leaving 
the  coarser  sandstones  to  form  almost  the  only  exposures  rising  above  the 
sand-plain  level.  For  this  reason  it  is  not  safe  to  make  any  distinction 
between  a  more  shaly  and  a  less  shaly  series  on  the  western  shore  of  the 
bay.  On  the  contrary,  it  is  very  likely  that  shales  also  form  an  important 
element  of  the  series  northward  and  westward,  away  from  the  shore  line, 
but  that,  on  accoimt  of  their  more  ready  erosion,  they  do  not  frequently 
appear  above  the  soil. 

On  account  of  the  far  greater  abundance  of  sandstones  among  the 
rocks  of  this  western  area,  so  typically  developed  in  South  and  North 
Kingstown,  than  in  the  Aquidneck  shales  farther  east,  the  name  Kingstown 
sandstones  is  suggested  for  this  western  complex  of  strata,  as  being  of  value 
in  designating  them  when  it  is  desirable  to  distinguish  the  two  formations 
where  they  are  typically  develoned.  The  Kingstown  sandstones  underlie 
the  Aqiiidneck  shales. 

Section  from  the  Bonnet  to  Boston  Neck. At  the  Bomiet  tllC   KlugStOWU   SerieS  dipS 

about  60°  E.,  giving  an  exposed  thickness  of  about  700  feet,  with  a  possible 
thickness  of  about  1,350  feet,  if  we  include  the  area  as  far  west  as  Wesquage 
Pond,  which  area,  although  without  exposures,  may  be  presumed  to  be  under- 
lain by  similar  rocks.  Judging  by  the  strikes  along  the  shore,  the  lowest 
part  of  this  section,  consisting  of  the  strata  supposed  to  underlie  the  eastern 
edge  of  Wesquage  Pond,  can  lie  only  a  short  distance  above  the  most 
eastern  exposures  on  Boston  Neck  and  at  the  South  Ferry.  The  most  eastern 
exposures  on  Boston  Neck  dip  nearly  vertically;  southeast  of  Watsons 
Pier  the  rocks  dip  60°  E.;  west  of  the  pier  they  dip  45°  E.;  three-quarters 
of  a  mile  northward,  15°  E.;  these  exposures,  with  the  intermediate  terri- 
tory, add  approximately  800  feet  to  the  section  already  given,  and  make 
a  total  of  2,150  feet  for  the  thickness  of  the  Carboniferous  section  from  the 
Bonnet  southward,  assuming  that  no  folding  has  taken  place. 

Section  from  the  Bonnet  to  Hazzard's  quarry  and    Indian  Corner. TllC  Strata  CXpOScd  aloUg 

the  shore  of  Boston  Neck  are  probably  repeated  north  of  South  Ferry, 
but  the  dips  here  are  low,  between  20°  and  40°  E.,  at  times  nearly  hori- 
zontal, so  that  until  much  more  accurate  field  work  is  done  the  strata  north 
and  south  of  the  Bonnet  can  not  be  strictly  compared  with  one  another. 
The  Bonnet  section  as  far  west  as  Wesquage  Pond  was  estimated  at  1,350 


334  GEOLOGY  OF  THE  NAEEAGANSETT  BASIN. 

feet.  The  sections  from  South  Feny  to  the  exposures  nearest  Saunders- 
town  can,  on  account  of  these  low  dips,  be  estimated  at  about  350  feet, 
making  a  thickness  of  1,700  feet  from  the  eastern  part  of  the  Bonnet  to 
Saunderstown.  As  the  strata  along-  the  shore  approach  Saunderstown  from 
the  south,  the  dip  along  the  strike  increases,  until  north  of  Saunderstown  it 
becomes  nearly  vertical.  Then  the  di]3S,  continuing  along  the  strike,  become 
35°  and  45°  E.,  but  in  the  section  across  Hazzard's  quarry  (PL  XXI)  and 
westward  to  the  top  of  Barbers  Height  the  prevailing  dip  varies  between  50° 
and  65°  E.,  adding  about  2,200  feet  to  the  1,700  feet  already  accounted  for, 
making  a  total  of  3,900  feet  for  the  section  between  the  eastern  part  of  the 
Bonnet  and  Barbers  Height.  To  this  must  be  added  at  least  1,600  feet 
more,  in  order  to  include  the  exposures  south  of  the  road  nearly  half  a 
mile  west  from  the  top  of  Barbers  Height,  making  a  total  section  of  5,500 
feet  for  the  thickness  of  the  Carboniferous  from  the  Bonnet  to  the  locality 
just  mentioned.  Making  allowance  for  the  change  in  the  strike  of  the  rocks 
toward  the  west  of  north,  on  going  northward,  a  thickness  of  at  least  3,600 
feet  must  be  added,  in  order  to  include  both  the  exposures  at  Indian 
Corner  and  those  at  the  locality  half  a  mile  south  of  the  corner,  east  of 
the  road,  so  that  an  estimate  of  9,100  feet  for  that  part  of  the  Saunderstown 
sandstone  series  exposed  on  the  western  shore  of  the  bay  would  be  A^ery 
moderate  if  the  strikes  and  dips  of  the  scattered  exposures  were  considered 
as  fairly  representing  the  general  structure  of  the  strata  beneath  the  soil. 
This  estimate  seems  excessive,  and  a  series  of  close  synclines  and  anticlines, 
or  of  faults,  may  be  imagined  in  order  to  reduce  it  to  more  moderate  dimen- 
sions. It  should,  however,  be  remembered  that  at  present  no  facts  are 
known  in  this  part  of  the  field  warranting  such  an  interpretation  of  the 
structures  actually  observed.  For  a  continuation  of  the  discussion  of  the 
thickness  of  the  Kingstown  series  in  the  southwestern  part  of  the  Narra- 
gansett  Bay  area,  see  page  336. 

Kingstown  series  in  southwestern  Cranston  and  western  Warwick. At    tlie    preSeut    Stage   of 

inquiry  it  does  not  appear  safe  to  make  many  statements  as  regards  the 
equivalency  of  the  Kingstown  group  north  of  East  Greenwich  to  rocks 
exposed  in  the  southern  part  of  the  field.  The  coarse  conglomeratic 
sandstone  at  Hills  Grove  may  belong  to  the  Saunderstown  series.  The 
mediiim-grained  sandstone  east  of  Hills  Grove  and  southwest  of  Norwood, 
with  its  bluish-gray  color,  is  very  similar  to  some  of  the  sandstones  exposed 


KINGSTOWN  SERIES  IN  CEANSTON  AND  WARWICK.  335 

along  the  road  1  and  2  miles  north  of  Wickford.  If  the  escarpment 
west  of  the  railroad  from  Wickford  Junction  to  East  Greenwich,  Coweset, 
Apponaug,  Natick,  and  northward,  marks  the  western  boundary  of  the 
Carboniferous  basin,  south  as  well  as  north  of  East  Grreenwich,  the 
equivalents  of  the  Saunderstown  sandstones  must  lie  immediately  east  of 
that  escarpment  in  Cranston  and  Warwick,  and  would  be  expected  to  show 
a  considerable  thickness  and  some  lithological  resemblance  to  the  exposures 
southward.  As  a  matter  of  fact,  however,  the  exposures  in  Warwick  are 
altogether  insufl&cient  to  afford  the  basis  for  a  judgment  on  this  point.  In 
southwestern  Cranston,  north  of  Natick  and  Pontiac,  sandstones  occur 
dipping  at  a  low  angle  to  the  eastward,  except  along  the  Carboniferous 
margin.  Beginning,  however,  near  the  State  almshouse  and  extending 
thence  northward  along  the  east  side  of  the  hill  occupied  in  part  by  the 
Reform  School  is  a  series  of  black  shales,  becoming  in  places  very  coaly. 
These  coaly  shales  are  the  conspicuous  feature  of  the  Carboniferous  section 
in  western  Cranston,  and  appear  in  the  mines  east  of  the  Sockanosset 
Reservoir  and  on  the  east  side  of  Rocky  Hill.  Beneath  the  coal-bearing 
shales  at  Sockanosset  Hill  are  others  of  dark-blue  or  black  color,  often 
ottrelitic,  which  are  exposed  in  the  vicinity  of  Sockanosset  Reservoir  and 
near  Waylaud  Station.  Associated  with  these  shales  are  sandstones,  but 
these  more  northern  sandstones  are  usually  bluish  gray,  or  more  or  less 
carbonaceous  and  medium  grained,  and,  although  not  very  different  from 
the  sandstones  farther  southward,  do  not  closely  resemble  them 

While,  therefore,  it  seems  beyond  qiiestion  that  the  rocks  of  western 
Warwick  and  Cranston  form  the  northern  extension  of  the  Kingstown  series, 
they  present  somewhat  different  lithological  features,  the  shales  being  much 
more  coaly,  and  at  one  horizon  containing  workable  coal;  moreover,  the 
sandstones  are  finer  grained  and  apparently  less  quartzitic  and  less  suggestive 
of  arkose.  Still,  while  the  more  carbonaceous  character  of  the  shale  north- 
ward is  recognized,  the  abundance  of  dark-blue  shales,  certainly  containing 
carbonaceous  material,  along  the  shore  southward  from  Barbers  Height 
to  the  Bonnet  should  not  be  forgotten.  The  more  northern  exposures,  in 
Cranston,  will  therefore  be  regarded  as  simply  a  more  carbonaceous  phase 
of  the  Saunderstown  series,  while  they  evidently  correspond  also  to  the 
lowest  part  of  the  lower  part  of  the  Tenmile  River  beds  or  the  Pawtucket 
shales  of  Mr.  Woodworth. 


336  GEOLOGY  OF  THE  NAERAGAlSrSETT  BASIN. 

Probable  thickness  of  the  Kingstown  sandstone  series  in  Cranston  and  Warwick. 1  lie   clipS   OI    tllG 

rocks  exposed  in  southwestern  Cranston  are  rather  low,  usually  varying 
from  nearly  horizontal  to  25°  NE.  and  E.  The  miners  report  a  steeper  dip 
in  the  mine  on  the  east  side  of  Sockanosset  Hill,  the  reported  inclination 
being  about  50°  E.;  but  this,  judging  from  surface  exposures,  seems  to  be 
but  a  local  increase  of  dip. 

On  the  eastern  side  of  Warwick  Neck,  toward  Rocky  Point,  the 
sandstones  forming  the  slopes  of  the  hill  dip  about  45°  E.  The  first 
sandstones  and  shales  met  on  the  road  to  Rocky  Point,  and  some  of  the 
sandstone  and  conglomerate  exposures  at  the  point  also,  slope  about  20°  E. 
Between  Hills  Grove  and  Norwood  Station  and  Warwick  Neck  there  are 
no  exposures.  Under  these  circumstances  it  is  not  safe  to  make  calcula- 
tions as  to  total  thickness  of  the  series  of  strata  underlying  Warwick  and 
Cranston;  but  with  an  average  inclination  of  20°  E.,  which  is  hardly  war- 
ranted, considering  the  often  lower  dips  where  the  rocks  are  actually 
exposed,  the  total  thickness  of  the  Carboniferous  series  from  southwestern 
Cranston  to  the  conglomerates  of  Rocky  Point  would  be  about  11,200 
feet.  The  actual  exposures  suggest  that  this  estimated  thickness  is  perhaps 
extravagant.     (See  pp.  334,  337.) 

If  a  series  of  close  synclines  and  anticlines  be  imagined  along  the 
western  margin  of  the  southern  part  of  the  bay,  extending  northward  into 
Warwick  and  Cranston,  the  preceding  estimate  can  hardly  be  said  to  have 
any  value  whatever.  In  that  portion  of  the  field  investigated  by  the  writer, 
limited  to  the  Narragansett  Bay  quadrangle,  there  is  no  actual  field  evidence 
of  such  folding,  either  north  or  south,  although  the  great  east-west  extension 
of  the  Kingstown  area  of  exposure  is  suggestive  of  such  folding. 

Warwick  Neck  exposures. — The  lowest  part  of  tlus  thickuess  of  11,200  feet  of 
Carboniferous  strata  in  Warwick  and  Cranston  is  equivalent  to  the  Kings- 
town series  as  exposed  farther  southward.  Whether  the  Warwick  Neck 
exposures  belong  to  the  Kingstown  series  can  not  be  determined  by  the 
evidence  secured  in  the  area  in  question.  Near  the  southern  end  of  Warwick 
Neck  carbonaceous  shales  occur  along  the  shore,  the  contortion  suggesting 
local  folding.  Black  shales  are  found  in  the  railway  cut  at  the  lower  end  of 
the  neck  Heavy  sandstone  beds,  some  medium  conglomerate  layers,  and 
dark-blue  shales  are  seen  on  the  eastern  side  of  the  neck,  with  more  bluish 
shale  on  the  east  before  reaching  the  conglomerate  series  of  Rocky  Point. 


KINGSTOWIJr  SERIES  EAST  OF  THE  BONNET.  337 

Lithologically  the  Warwick  Neck  exposures  could  be  readily  associated 
with  the  northern  extension  of  the  Kingstown  series  as  exposed  in  south- 
western Cranston,  and  might  therefore  be  considered  as  forming  part  of  the 
same  series.  They  would  constitute  in  that  case  the  upper  portion  of  the 
Kingstown  series  in  the  northwestern  part  of  the  Narragansett  Bay  area. 
This  would  make  the  Warwick  Neck  and  Rocky  Point  exposures  roughly 
equivalent  to  the  more  eastern  exposures  mentioned  in  the  following 
paragraphs. 

Exposures  on  the  western  islands  of  the  bay. Tlie    KiugStOWU     SerieS     appCarS    tO     be 

not  hmited  to  the  western  shores  of  the  bay.  The  strata  exposed  on  (1) 
Dutch  Island,  at  (2)  Beaver  Head  on  Conanicut  Island,  toward  the  south 
of  Dutch  Island,  (3)  north  of  Round  Swamp  on  the  northern  half  of  the 
island,  (4)  on  Hope  Island,  and  (5)  along  the  western  shore  of  Prudence 
Island,  north  of  the  wharves,  all  seem  to  belong  to  this  series. 

Thickness  of  strata  between  the  Bonnet  and  Dutch  Island. The  UCarCSt  poiut  of  apprOacll 

of  the  island  exposures  with  those  on  the  west  shore  is  between  Dutch 
Island  and  Saunderstown,  where  they  are  distant  4,200  feet.  Beaver  Head 
is  about  5,400  feet  from  Sonth  Ferry,  and  the  most  western  part  of  northern 
Conanicut  is  6,000  feet  distant  from  the  Hazzard  quarry  region  north  of 
Saunderstown.  While,  therefore,  it  may  appear  rash  to  associate  in  one  geo- 
logical series  strata  so  far  disconnected,  other  facts  make  this  relation  more 
than  probable.  Tracing  the  rocks  of  the  Bonnet  section  northward  on  the 
map,  in  accordance  with  the  suggestions  offered  by  the  actual  strikes  of  the 
rocks  exposed  along  the  shore,  it  will  be  seen  that  the  northward  extension  of 
the  Bonnet  series  must  lie  a  considerable  distance  toward  the  east  of  Saun- 
derstown, while  the  southern  extension  of  the  Dutch  Island  strata  would 
approach  the  western  shore  at  the  Bonnet.  Traced  in  this  way  the  Bonnet 
section  is  found  to  approach  the  Dutch  Island  section  within  1,350  to  1,750 
feet.  Assuming  a  dip  of  60°  for  this  unexposed  part  of  the  section,  the 
Bonnet  section  underlies  the  Dutch  Island  section  from  1,200  to  1,500  feet. 
The  dips,  however,  on  the  Saunderstown  shore  opposite  the  island  do  not 
exceed  40°,  while  the  western  shore  dips  of  Dutch  Island  are  also  usually 
less  than  50°,  so  that  the  two  sections  may  possibly  approach  each  other 
within  975  to  1,200  feet.  Considering  this  moderate  interval  of  unknown 
strata,  and  the  absence  of  any  signs  to  the  contrary,  the  lithological  simi- 
MON  xxxiii ii2 


338  GEOLOGY  OF  THE  NAERAGANSETT  BASIK 

larity  of  the  Dutch  Island  rocks  and  the  Kingstown  sandstone  series  may 
be  regarded  as  conclusive  of  their  close  geological  relationship. 

The  Dutch  Island  exposures  must  therefoi'e  be  added  to  the  sections 
exposed  on  the  mainland  in  order  to  form  an  estimate  of  the  total  thickness 
of  th  Kingstown  series  in  the  southwestern  part  of  the  Narragansett  Bay 
region.     This  is  discussed  more  fully  in  the  third  paragraph  following. 

Lithoiogy  of  the  Dutch  Island  series. — lu  general,  tlic  Strata  of  Dutch  Island  may 
be  described  as  consisting  chiefly  of  sandstones  with  subsidiary  conglom- 
erate layers,  underlain  on  the  western  side  of  the  island  by  a  series  in 
which  black,  often  very  cai'bonaceous,  shales  predominate.  Considering 
the  black  color  of  some  of  the  Bonnet  shales,  the  Carbonaceous  character 
of  the  fern-bearing  shales  on  Dutch  Island  is  not  unexpected.  The  con- 
glomerate layers  evidently  contain  larger  pebbles  than  most  of  the  conglom- 
erates found  high  up  in  the  series  on  the  western  side  of  the  bay,  but  it  is 
evident  that  their  length  is  largely  due  to  stretching.  The  pebbles  are  also 
less  qnartzitic  than  lower  down.  But  it  is  the  considerable  abundance  of 
sandstones  in  the  Dutch  Island  section  that  suggests  relationship  with  the 
Kingstown  series. 

Beaver  Head  section. — At  Beavcr  Head,  couglomeratc  is  exposed  only  on  the 
western  border  of  the  hill,  near  low-water  mark.  The  main  mass  of  the 
hill  is  evidently  composed  of  black  shales,  with  intercalated  subsidiary 
thin  sandstone  beds  and  some  arkose.  The  shales  are  decidedly  carbona- 
ceous. The  Beaver  Head  section  is  evidently  an  introduction  to  the  Aquid- 
neck  shale  series  as  exposed  farther  eastward  on  the  island,  and  seems  to 
have  its  likeness  in  the  carbonaceous  shales  at  the  base  of  the  shale  series 
on  the  western  side  of  Prudence  Island. 

Total  thickness  of  the  Kingstown  series,  including  the  conglomerate  at  Beaver  Head. Taking      40*^ 

as  an  average  of  the  eastward  dips  on  Dutch  Island,  the  thickness  of  the 
Dutch  Island  section  is  about  1,050  feet;  this,  added  to  the  unknown  inter- 
val of  975  to  1,200  feet  occupied  by  the  western  passage  (see  bottom  of  pre- 
ceding page)  and  the  estimated  thickness  of  9,100  feet  for  the  series  as 
exposed  on  the  western  shores  of  the  bay  from  the  Bonnet  to  Hazzard's 
quarry,  Indian  Corner,  and  southward  (see  pp.  333  and  334),  would  give 
a  thickness  of  from  11,125  to  11,350  feet  for  the  whole  series  of  Kingstown 
sandstones,  including  Dutch  Island.  An  additional  thickness  of  225  feet 
would  probably  include  the  conglomerate  layers  exposed  at  low  tide  on  the 
western  margin  of  Beaver  Head,  so  that  11,500  feet  would  express,  in  round 


KINGSTOWN  SERIES  OF  NORTHERN  CONANICUT.  339 

numbers,  the  total  thickness  of  the  Kingstown  series  in  the  southwestern 
part  of  the  Narragansett  Bay  area.  It  will  be  remembered  that  in  the 
northwestern  part  of  this  area,  in  Warwick  and  Cranston,  the  estimated 
thickness  was  11,200  feet  (see  p.  336). 

Western  shore  of  conanicut. — The  rocks  along  the  wcstem  shore  of  Conanicut 
also  bear  considerable  resemblance  to  the  Kingstown  series  as  exposed  on 
the  mainland,  owing  to  the  presence  of  abundant  sandstones,  but  they  are 
still  more  similar  to  the  strata  exposed  on  Dutch  Island,  of  which  they  are 
probably  the  continuation.  Along  the  shore  opposite  Slocum  and  Great 
ledges  there  is  considerable  coaly  shale,  some  of  which,  according  to  T.  N. 
Dale,^  contains  fern  impressions.  There  is  also,  an  abundance  of  sandstone, 
interbedded  with  which  are  subsidiary  conglomerate  layers  with  very  much 
elongated  pebbles,  bearing  considerable  resemblance  lithologically  to  the 
conglomerate  of  Dutch  Island  and  the  layer  on  the  western  margin  of 
Beaver  Head.  The  strikes  along  these  ledges  practically  follow  the  shore. 
From  Sand  Point  northward  similar  coaly  shales  and  sandstones  with 
subsidiary  conglomerate  layers  are  exposed.  The  strike  is  nearly  N.  3°  E. 
Along  the  entire  Avestern  shore  the  dips  are  eastward,  usually,  however, 
quite  low. 

Eastern  shore  of  Conanicut. — Wliilc  tlic  cxposures  aloug  thewestcm  shore  of 
northern  Conaniciit  can  be  safely  correlated  with  the  strata  on  Dutch  Island 
and  western  Beaver  Head,  the  position  and  geological  structure  of  the  strata 
forming  the  middle  and  eastern  parts  of  Conanicut  remain,  to  say  the  least, 
problematical.  East  of  North  Point  occur  coaly  shales,  apparently  showing 
lateral  squeezing  from  east  to  west.  Along  the  eastern  shore  are  found 
coaly  shales,  at  one  point  with  fern  impressions;  also  gray  sandstones.  The 
strikes  average  N.  10°  E.,  and  the  dip  is  usually  very  steep,  nearly  vertical, 
but  shows  in  places  sudden  variations  which  can  most  readily  be  reconciled 
with  crumpling.  The  cleavage  often  obsciires  the  bedding.  The  absence 
of  conglomerate  layers  along  the  eastern  shore  is  a  conspicuous  feature  in 
contrast  with  the  more  western  line  of  exposures,  including  western 
Conanicut,  Dutch  Island,  and  Beaver  Head.  The  exposures  along  the  east- 
ern shore  of  noi-thern  Conanicut  may  therefore  belong  to  another  horizon, 
possibly  a  higher  one  corresponding  to  the  strata  overlying  the  conglom- 
erates on  the  western  margin  of  both  Beaver  Head  and  Prudence  Island. 

'  On  metamorphism  iu  the  Rhode  Island  coal  basin :  Proc.  Newport  Nat.  Hist.  Soc,  Doc.  3,  1885, 
pp.  85-66. 


340  GEOLOGY  OF  THE  NAREAGANSETT  BASIN. 

Probablefoldingin  the  northern  part  of  Conanicut  Island. Tlie   clifficultieS   of    tllG     pi'Oblem 

may  be  briefly  stated  as  follows:  The  green  sliales  of  the  southern  half  of 
Conanicut  make  their  first  appearance  at  the  southern  end  of  the  lagoon 
east  of  Beaver  Head.  From  this  point  they  extend  in  a  direction  N  37°  E. 
to  the  eastern  shore  of  the  island,  being  last  seen  at  a  point  a  mile  north  of 
Freebodys  Hill.  The  highest  layer  of  conglomerate  at  Beaver  Head  occurs 
a  little  above  low-water  mark  on  the  extreme  western  shore  of  the  head- 
land. The  next  most  eastern  exposure  of  conglomerate  northward  lies 
along  the  most  western  part  of  the  shore  of  Conanicut,  northwest  of  Round 
Swamp.  The  second  locality  lies  about  N.  10°  E.  from  the  first.  The 
average  strike  of  the  sandstones,  coaly  shales,  and  conglomerate  beds  on 
the  western  side  of  northern  Conanicut  is  not  more  than  N.  10°  E.,  which 
seems  to  suggest  a  connection  between  the  Beaver  Head  conglomerate  and 
the  conglomerates  farther  northward.  In  that  '"ase,  however,  there  is  a 
divergence  of  about  27°  between  the  conglomerate  layers  on  the  west  and 
the  green  shales  on  the  east,  which  suggests  a  thickening  of  the  intervening 
strata  northward,  an  unconformity,  a  peculiar  form  of  fan-shaped  folding, 
or  a  fault.  There  is,  however,  no  good  geological  evidence  for  any  one  of 
these  suggestions. 

Curiously  enough,  the  strikes  on  the  eastern  side  of  Conanicut,  north 
of  the  latitude  of  southern  Gould  Island,  are  also  N.  10°  E.  This  makes  it 
difficult  to  imagine  the  precise  nature  of  a  system  of  folding  which  would 
give  such  an  increase  of  area  in  an  east-west  direction  northward  as 
has  been  just  described,  and  which  nevertheless  could  escape  detection  in 
the  regions  where  actual  exposures  occur.  The  strata  on  the  western  shore 
of  northern  Conanicut  dip  eastward  at  a  low  angle.  On  the  eastern  shore, 
north  of  the  latitude  of  southern  Gould,  Island,  the  dips  appear  very  varia- 
ble, being  sometimes  almost  vertical.  These  steep  dips  may  be  an  expres- 
sion of  that  folding  which  must  also  obtain  over  the  middle  length  of  the 
island,  in  order  to  reconcile  the  apparent  divergence  of  the  conglomerate 
layers  and  the  green  shales  as  described  above,  without  recognizing  a 
marked  increase  in  the  thickness  of  the  strata  involved  or  any  possibility  of 
faulting  or  of  an  unconformity.  The  facts  observed  elsewhere  in  the  field 
do  not  warrant  the  assumption  of  a  great  unconformity  here,  but  the  possi- 
bility of  faulting  must  not  be  precluded. 

If  the  possibility  of  a  faiilt  starting  somewhere  northeast  of  Beaver 


KINGSTOWN  SERIES  ON  HOPE  ISLAND.  341 

Head  and  increasing  toward  Round  Swamp  and  beyond  be  excluded,  a 
low  general  eastward  dip  of  a  series  of  strata,  subjected  to  abundant  sub- 
sidiary folding,  pitching  southeastward  along  their  southern  border,  is  the 
only  explanation  that  occurs  to  the  writer,  and  very  much  more  field  work 
is  necessary  to  form  anything  like  a  safe  opinion  on  this  point.  In  the 
absence  of  more  accurate  information  an  estimate  of  the  maximum  thick- 
ness of  the  strata  involved  in  the  northern  Conanicut  complex  seems  unwar- 
ranted. The  thickness  certainly  amounts  to  as  much  as  1,735  feet,  but  it 
may  many  times  exceed  this. 

Hope  Island. — Llthologically  the  rocks  forming  Hope  Island  resemble  the 
strata  exposed  on  the  western  shore  of  the  bay  more  closely  than  the  more 
northern  exposures  along  the  western  side  of  northern  Conanicut.  This 
may  be  due  in  part  to  the  greater  metamorphism  of  the  Hope  Island  rocks. 
The  sandstone  here  is  often  quartzitic,  of  white  color,  and  contains 
biotitic  mica.  The  interbedded  fine-grained  sandstones  are  usually  very 
black.  Black  shales  are  found  only  along  the  western  and  northern  sides 
of  the  island,  and  form  evidently  the  lower  beds  of  the  small  section  here 
involved.  The  quartzitic  sandstones  contain  scattered  pebbles  and  thin 
conglomeratic  layers.  Conglomerates  are  present  to  a  certain  degree  in 
all  the  sandstone  layers.  On  the  western  side  of  the  island  they  are  a  minor 
feature,  while  on  the  eastern  side  they  form  half  the  rock.  The  pebbles 
are  uniformly  small,  usually  not  over  IJ  inches  in  diameter.  Many  of 
them  are  decidedly  quartzitic  or  granitic.  There  has  been  little  flattening 
of  the  pebbles  by  shearing.  The  strike  over  the  southern  three-fourths  of 
the  island  averages  N.  30°  E.,  with  an  easterly  dip  of  60°  to  80°  on  the 
western  side,  and  a  dip  of  30°  to  45°  E.  on  the  eastern  shore.  These 
strikes  also  suggest  that  the  Hope  Island  section  may  underlie  the  exposures 
on  the  western  shore  of  northern  Conanicut,  notwithstanding  the  northerly 
strikes  of  the  latter.  The  section  exposed  on  the  island  is  estimated  to  have 
a  thickness  of  at  least  800  feet. 

At  the  northern  end  of  Hope  Island  the  dip  of  the  strata  is  very  low 
to  the  northeastward.  Were  it  not  for  this  fact  the  more  southern  strikes 
would  carry  these  strata  approximately  toward  Pine  Hill  and  Gull  points, 
on  northern  Prudence  Island.  The  outlines  of  the  coast  and  the  trends  of 
the  main  hills  on  northern  Prudence  Island  and  on  Patience  Island  suggest 


342  GEOLOGY  OF  THE  NAEEAGA^J^SETT  BASIN. 

a  strike  toward  the  west  of  north  for  the  underlying  strata,  which  would 
agree  with  the  exposures  at  Rocky  Point. 

Kingstown  series  exposures  on  the  western  islands. FrOUl    tllO     BoUUet     tllC     KingStOWU 

series  has  been  traced  iiorthward  into  western  Warwick  and  southwestern 
Cranston.  The  relationship  of  the  overlying  Dutch  Island  section  has  been 
shown,  and  similar  rocks  have  been  traced  along,  the  Avestern  part  of  north- 
ern Conanicut,  and  others  form  Hope  Island.  The  exposures  at  Beaver 
Head  and  along  the  eastern  shore  of  northern  Conanicut  appear  to  be  a 
more  coaly  variation,  intermediate  between  the  sandstone  series  beneath  and 
the  green  and  dark-blue  shales  above. 

Prudence  Island. — Litliologically  somewliat  similar  features  are  presented 
along  the  western  side  of  Prudence  Island,  where  sandstones  and  some  con- 
glomerate occur  along  the  shore  north  of  Prudence  Park  wharf,  dipping- 
eastward,  on  the  average,  about  25°.  Overlying  these  are  black  carbona- 
ceous shales  and  sandstones  containing  fern  leaves.  Higher,  near  the 
wharf,  are  shown  the  dark-blue  shales.  If  the  dark-blue  shales  be  corre- 
lated with  the  green  and  dark-blue  shales  of  Conanicut,  and  if  the  sand- 
stones and  conglomerates  be  associated  with  the  Kingstown  series  as 
shown  on  Dutch  Island,  then  the  coaly  shales  are  equivalent  to  the  black 
shales  forming  the  main  mass  of  Beaver  Head.  Comparisons  at  so  great 
distances  have,  of  course,  little  value.  The  real  reason  for  considering  the 
sandstones  and  conglomerates  of  the  western  shore  of  Prudence  Island  as 
equivalent  to  the  top  of  the  Saunderstown  series  is  their  situation  beneath 
a  considerable  thickness  of  shales.  The  thickness  and  lithological  charac- 
teristics of  these  shales  seem  to  warrant  their  correlation  with  the  great 
body  of  shales  on  Aquidneck  Island  and  the  southern  part  of  Conanicut 
Island,  the  whole  forming  a  geological  group  in  the  bay  region  of  the  Nar- 
ragansett  Basin,  winch  group  is  here  called  the  Aquidneck  series,  and 
which  overlies  the  Kingstown  series.  The  unity  of  the  shale  series  will  be 
discussed  further  on.  Correlating  the  conglomerates  on  the  western  shore 
of  Prudence  Island  with  the  conglomerate  at  Beaver  Head,  it  may  be  sug- 
gested that  the  sections  at  Rocky  Point  may  not  far  underlie  their  horizon. 

The  actual  exposure  of  sandstones  and  conglomerates  north  of  the 
wharf  at  Prudence  Park  can  hardly  exceed  50  feet.  The  overlying  coaly 
shales  may  possibly  amoimt  to  150  feet  in  thickness  south  of  Prudence 
Park  wharf,  but  if  that  is  the  case  they  certainly  thin  out  rapidly  north- 


KINGSTOWN  SERIES  OP  WESTERN  BRISTOL  NEOK.  343 

ward,  since  the  more  northern  exposures  on  the  island  show  that  the  sand- 
stones and  conglomerates  are  overlain  l^y  the  dark-bluish  shale,  with  only 
a  small  interval  of  unknown  rock.  The  most  ready  interpretation  of  this 
fact  is  to  suppose  that  the  lower  part  of  the  Aquidneck  shales  is  often  coaly, 
the  thickness  of  this  coaly  section,  however,  being  greatly  variable. 

Western  Bristol  Neck. — Bluisli  aud  grceuish  Aquldueck  shales  form  the  main 
mass  of  the  Carboniferous  rocks  on  Bristol  Neck.  Underlying  them  on 
the  southwest  is  a  thick  bed  of  sandstone,  amounting  to  perhaps  50  feet 
About  225  feet  beneath  this  bed  occurs  more  sandstone,  of  dark  color,  con- 
taining coaly  matter,  and  perhaps  150  feet  beneath  this  level  is  coaly  shale 
with  fern-leaf  and  Annularia  impressions.  If  the  eastward  dip  of  20°  is 
maintained,  the  conglomerate  exposed  at  two  localities  above  the  main  sand- 
stone bed  first  mentioned  lies  about  250  feet  above  the  latter.  A  short 
distance  above  the  conglomerate  begin  the  greenish  and  dark-blue  shales 
of  the  Aquidneck  series.  The  order  of  succession  on  the  western  side  of 
Bristol  Neck  is,  therefore:  coaly  shale,  gray  or  darker  sandstone,  bluish 
sandstone,  conglomerate  with  large  pebbles,  greenish  and  dark-blue  shales. 
If  the  great  shale  series  of  Bristol  Neck  be  correlated  with  the  shales  of 
Prudence  Island  and  southern  Conanicut,  the  underlying  rocks  may  repre- 
sent the  upper  part  of  the  Kingstown  series.  Certain  facts  suggest  a 
relationship  with  at  least  the  Prudence  Island  section.  Pebbles  containing 
oboli  are  foimd  in  the  conglomerate  on  the  west  side  of  Prudence 
Island.  While  the  pebbles  of  the  conglomerate  on  the  west  side  of  Bristol 
Neck  are  of  much  larger  size,  their  lithological  character  agrees  very  well 
with  that  of  the  Prudence  Island  pebbles,  and  oboli  will  no  doubt  be 
eventually  found  there  also.  There  is  a  considerable  section  of  sandstone 
on  the  west  side  of  Bristol  Neck.  It  is  not  interbedded  with  the  con- 
glomerate, but  is  found  beneath  it.  The  coaly  shale  on  Bristol  Neck,  as 
well  as  that  on  Prudence  Island,  contains  plants,  but  the  coal}^  shale  on 
Bristol  Neck  occurs,  not  at  the  base  of  the  greenish  and  dark-blue  shales, 
but  below  the  sandstones  and  conglomerates  of  that  field.  As  a  matter  of 
fact,  however,  these  latter  belong  very  high  in  the  Kingstown  series,  and 
strict  parallelism  of  strata  could  hardly  be  expected  at  so  great  a  dis- 
tance as  that  from  Prudence  Park  to  western  Bristol  Neck,  in  a  geological 
field  where  lithological  changes  along  the  strike  are  frequent.  Only  a 
general  accordance  could  be  demanded.     For  this  reason  the  coaly  shales, 


344  GEOLOGY  OF  THE  NAEEAGANSETT  BASIN. 

sandstones,  and  conglomerate  of  western  Bristol  Neck  are  considered  as 
belonging  at  the  top  of  the  Kingstown  seiies.  The  sandstone  exposures 
on  Popasquash  Neck  probably  belong  to  the  same  horizon. 

Rumstick  Neck. — Tlic  green  shales  of  Rumstick  Neck  resemble  the  green 
shales  of  western  Bi-istol  Neck  and  some  of  those  of  Prudence  Island. 
The  sandstone  underlying  the  same,  offshore  toward  the  southwest,  contains 
plant-stem  impressions  similar  to  those  found  in  the  sandstones  beneath 
the  shales  on  the  western  side  of  Prudence  Island  The  curve  of  the 
strike  of  the  sandstones  suggests  a  shallow  syucline  pitching  northward,  and 
a  similar  curve  in  the  strike  of  the  chief  sandstone  bed  on  the  southwest 
side  of  Bristol  Neck  suggests  a  similar  structure  there.  The  exposure  on 
Rumstick  Neck  is,  however,  too  isolated  to  be  safely  correlated. 

Kingstown  sandstones  equivalent  to  the  lower  part  of  the  Coal  Measures  group, Jli    the  StnkeS  Of 

the  coaly  shales,  the  sandstones,  and  the  conglomerates  on  the  western 
side  of  Bristol  Neck  be  continued  for  any  considerable  distance  northward, 
rocks  referred  by  Mr.  Woodworth  to  the  Seekonk  section  will  be  met.  The 
Kingstown  series  would  therefore  seem  to  correspond  to  the  lower  part  of  the 
Coal  Measures,  including  the  Seekonk  group,  as  limited  by  Mr.  Woodworth 
farther  northward. 

Triangular  area  of  the  Kingstown  series  in  the  Narragansett  Basin,  narrowing  southward. PrOvided 

that  all  the  correlations  so  far  made  are  correct,  the  following  fact  is  brought 
out.  In  the  latitude  of  the  Bonnet  the  Kingstown  series  occupies  a  width 
of  3|  miles.  The  eastern  margin  of  the  area  occupied  turns  northeastward 
at  Beaver  Head,  with  a  direction  of  N.  38°  E.,  as  far  as  the  eastern  side 
of  Conanicut.  At  the  latitude  of  Hammond  Hill  the  series  occupies  a 
width  of  at  least  5  miles.  At  Hammond  Hill  the  western  margin  of  the 
area  turns  northwestward,  and  in  the  neighborhood  of  Wickford  Junction 
the  width  of  the  area  is  about  8^  miles.  According  to  this  measurement 
the  eastern  border  of  the  area  takes  a  more  northerly  course  along  the 
east  side  of  northern  Conanicut.  From  Wickford  Junction  the  western 
border  extends  N.  23°  E.  to  East  Grreenwich,  and  the  eastern  border  N. 
24°  E.  along  western  Prudence  Island  to  the  eastern  side  of  Popasquash 
Neck.  The  width  of  the  Kingstown  area  at  East  Greenwich,  according  to 
this,  is  8  miles.  Nox'th  of  Coweset  the  western  margin  extends  in  a  north- 
western direction  as  far  as  southern  Cranston,  and  thence  N.  10°  E.  The 
eastern  margin  may  extend  northward  along  the  western  side  of  Warren 


THICKNESS  AND  POLDmG  OP  KINGSTOWN  SERIES.  345 

River.  In  that  case  the  area  invoh^ed  has  a  width  of  at  least  10  miles  at 
the  northern  limit  of  the  Narragansett  Bay  map. 

The  increase  in  the  width  of  the  area  occnpied  by  the  Kingstown  series 
from  3 1  miles  on  the  sonth  to  10  miles  on  the  north  is  of  course  striking 
and  demands  some  explanation. 

Thickness  of  the  series  and  evidence  of  folding. The    tlllckneSS   of    tllC     SeHeS     Can     be 

measured  with  the  greatest  degree  of  certainty  at  its  southern  end,  where 
exposures  are  frequent  and  dips  are  steep.  The  total  thickness  of  11,500 
feet  there  indicated  may  not  equal  that  of  the  formation  farther  northward. 
The  steep  dips  in  the  area  immediately  north  of  a  line  connecting  Quonset 
Point,  Wickford,  and  Wickford  Junction,  for  instance,  suggest  a  greater 
thickness.  So  does  the  great  east-west  extension  of  the  formation 
northward.  Unless  in  spite  of  the  apparent  uniformity  of  strikes  and  dips 
over  large  areas  there  be  in  reality  a  system  of  repetition  dufe  to  folding, 
the  thickness  of  the  Kingstown  sandstone  group  must  in  places  greatly 
exceed  11,500  feet.  There  is  a  little  evidence  in  favor  of  such  folding  in 
the  portion  of  this  region  actually  occupied  by  the  Kingstown  sandstones: 
(1)  Along  the  eastern  side  of  Providence  River,  north  of  Riverside  occurs 
a  synclinal  fold,  but  this  seems  to  disappear  northward.  (2)  At  Rumstick 
Neck  and  on  the  southwestern  side  of  the  Aquidneck  shale  area  on  Bristol 
Neck  the  trend  of  the  underlying  sandstones  suggests  synclinal  folding. 
(3)  Prudence  Island  is  a  case  of  a  well-marked  synclinal  fold.  (4)  The 
steep  dips,  varying  suddenly  to  lower  inclinations,  on  the  northwestern  side 
of  Conanicut  suggest  crumpling  of  strata  and  possible  folding.  (5)  The 
shale  area  of  southern  Conanicut  has  evidently  suffered  folding,  but  the 
character  of  this  folding  has  not  been  well  worked  out.  (6)  Folds  are 
known  in  various  parts  of  Aquidneck  Island  All  of  these  facts  suggest 
folding  also  in  the  more  western  area  occupied  by  the  Kingstown  sandstones, 
but  the  direct  evidence  in  favor  of  such  folding  is  still  wanting. 

The  view  that  the  thickness  of  the  sandstone  series  northward  probably 
does  not  greatly  exceed  11,500  feet  is  also  supported  by  the  very  low 
general  inclination  of  the  strata  over  considerable  areas,  which  tends  to 
reduce  the  estimates  made  in  conformity  with  regions  where  the  dip  is 
steeper.  The  very  low  general  dips  of  most  of  southwestern  Cranston  and 
Warwick  have  already  been  mentioned. 

The  dips  on  the  western  side  of  Bristol  Neck  are  comparatively  low. 


346  GEOLOGY  OF  THE  NA.REAGANSETT  BASIN. 

This  is  also  true  of  the  inclination  of  the  strata  on  the  westeni  side  of 
Prudence  Island  and  on  the  western  side  of  Conanicut.  The  shale  series 
east  of  Mackerel  Cove  and  on  Freebodys  Hill  seems  also  to  have  low  dips. 
North  of  Barbers  Height,  toward  Hamilton  and  northwestward,  the  dips 
also  become  lower,  indicating  a  greater  horizontal  extension  of  the  series 
for  the  same  thickness  of  strata  than  exists  farther  southward.  The  evi- 
dence on  Potowomut  Neck  is  in  favor  of  low  dips. 

If  these  areas  of  low  dips  among  those  of  higher  dips  can  be  con- 
sidered as  evidences  in  favor  of  a  system  of  local  folding,  at  present  only 
obscurely  known,  it  will  not  be  necessary  to  assign  any  extravagant  thick- 
ness to  the  more  northern  portion  of  the  Saunderstown  series. 

Rocky  Point  conglomerate  and  its  connection  with  the  estimate  of  the  thickness  of  the  northern  section. 

Unfortunately,  the  estimate  of  11,200  feet  for  the  Kingstown  series  in  south- 
western Craftston  and  in  Warwick  does  not  offer  a  means  of  comparison 
with  the  more  southern  section  noted  above,  because  (1)  it  does  not  include 
the  Rocky  Point  conglomerates,  supposing  that  the  latter  lie  at  the  top 
of  the  Kingstown  sandstone  series,  and  (2)  it  is  not  determinable  that  the 
rocks  immediately  beneath  the  Rocky  Point  conglomerates  belong  to  the 
sandstone  series,  for  the  reason  that  the  age  of  the  Rocky  Point  conglom- 
erate is  not  known  with  certainty.  In  the  field  investigated  by  the  writer 
there  is  no  evidence  militating  against  the  belief  that  these  conglomerates 
correspond  to  those  which  begin  to  occur  near  the  top  of  the  Aquidneck 
shales  as  exposed  northeast  of  Warren,  and  which  are  there  an  introduc- 
tion to  the  Dighton  conglomerates.  In  the  area  north  of  that  investig'ated 
by  the  writer,  the  Rocky  Point  conglomerates,  or  rather  their  supposed 
equivalents,  seem  to  occur  at  a  horizon  corresponding  more  nearly  to  the 
top  of  the  Kingstown  sandstone  series,  similar  to  the  conglomerate  of 
western  Bristol  Neck  and  western  Prudence  Island.  This  is  equivalent  to 
placing  them  on  the  horizon  of  the  Seekonk  group  of  Mr.  Woodworth, 
which  includes  also  the  series  of  shales,  sandstones,  and  medium  conglom- 
erates into  which  the  Aquidneck  shales  merg-e  north  of  Warren. 

Chief  features  of  the  Kingstown  series. TllC     KiugStOWU    SaudstOnC    SCricS    may  bc 

desci'ibed  as  a  complex  consisting  of  alternations  of  shale,  sandstone,  and 
conglomerates.  The  conglomerates  are  usually  made  up  of  very  small 
pebbles.  Near  the  base  of  the  section,  however,  in  the  basal  arkoses  and 
associated  rocks  there  occur  layers  with  large  pebbles.     Toward  the  top  of 


FOSSILS  IN  KINGSTOWN  SEEIES.  347 

the  section  conglomerates  come  in  again.  These  are  seen  at  the  western 
margin  of  Beaver  Head,  0:1  Dutch  Island,  the  western  side  of  northern 
Conanicut,  the  western  side  of  Prudence  Island,  and  the  western  side  of 
Bristol  Neck;  and  apparently  the  conglomei-ates  at  Rocky  Point  and  the 
eastern  side  of  Providence  River  belong  at  this  horizon.  (See  the  para- 
graph on  the  equivalence  of  tlie  Kingstown  and  Aquidneck  series,  on 
p.  361.) 

Fossil-plant  localities, — Coaly  slialcs  witli  fem  impressions  occur  .as  follows: 
About  2,000  feet  above  the  base  of  the  series  are  the  coaly  shales  of 
Sockanosset  Hill,  inclosing  fern  leaves.  At  the  top  of  the  series  and  at 
several  points  farther  down  are  more  carbonaceous  shales,  also  containing 
fern  impressions.  The  highest  beds  with  plant  remains  in  the  Kingstown 
series  are  the  conglomerate  and  sandstone  beds  exposed  on  the  western 
side  of  Prudence  Island.  The  coaly  shales  just  above  belong  to  the  base 
of  the  Aquidneck  bed.  On  Beaver  Head  the  shales  in  the  upper  part  of 
the  Kingstown  series  do  not  preserve  the  fern  impressions.  The  fossil 
locality  on  the  eastern  side  of  northern  Conanicut  probably  belongs  a  little 
above  this  horizon.  A  slightly  lower  horizon  is  occupied  by  the  exposm'e 
of  fern-bearing  coaly  shales  on  the  west  side  of  Bi'istol  Neck.  A  still  lower 
one  includes  the  fossil-fern  locality  on  the  western  side  of  Dutch  Island  and 
the  locality  discovered  by  Prof  T.  Nelson  Dale  on  the  western  side  of 
northern  Conanicut.  A  comparison  of  the  ferns  from  the  upper  and  lower 
horizons  might  show  variations  in  the  flora,  giving  suggestions  as  to  means 
of  recognizing-  the  same  horizons  observed  in  the  field. 

Plant  stems  are  found  above  the  level  of  the  lowest  coal  horizon  at 
Hills  Grove  and  near  the  top  of  the  section  on  the  western  side  of  Prudence 
Island,  and  possibly  the  exposures  off  the  end  of  Rumstick  Neck  and  along 
Providence  River,  in  all  cases  consisting  of  sandstones  belonging  to  the 
same  horizon.  Indeed,  the  upper  half  of  the  Tenmile  River  section  of 
Mr.  Woodworth  appears  to  be  in  places  rich  in  calamites. 

Ferns  occur  again  in  the  overlying  Aquidneck  shale  series  and  in  the 
coaly  shales  interbedded  with  the  coarse  conglomerate  series  at  the  top  of 
the  Narragansett  Basin  Carboniferous  section  at  Castle  Hill,  as  will  be 
described  later,  demonstrating  that  all  of  the  exposures  here  described,  from 
the  basal  conglomerates  and  arkoses  to  the  top  of  the  Purgatory  conglom- 
erate, are  Carboniferous. 


OHAPTEKA^III. 
THE  AQUIDNECK  SHALES. 

AREA  OCCUPIED  BY  THE  AQUIDN^ECK   SHAEE  SERIES. 

East  of  the  complex  of  rocks  called  the  Kingstown  sandstones,  owing  to 
the  characteristic  and  frequent  appearance  of  sandstone  beds  in  the  section, 
lies  an  equally  great  area,  in  which  shales  form  almost  all  of  the  exposures, 
excepting  where  synclinal  folding  has  allowed  an  overlying  conglomerate  to 
be  locally  preserved.  The  shales  of  this  eastern  area  contain  isolated  sand- 
stones and  thin  conglomerate  beds,  but  the  latter  are  so  rare  that  the  term 
"shale  series"  has  peculiar  force  in  designating  the  general  lithological 
character  of  the  rocks  in  question.  The  shales  occupy  (1)  the  southern  half 
of  Conanicut  Island  as  far  north  as  Round  Swamp,  excepting  (a)  the  small 
area  included  in  Fox  Hill,  already  described  as  the  top  of  the  Kingstown 
section,  and  (b)  a  small  area  of  arkose  on  the  east  side  of  Mackerel  Bay, 
north  of  the  granite  hills.  They  form  (2)  the  southern  and  larger  division 
of  Prudence  Island  (PI.  XXIII),  excepting  the  western  margin  of  the  island, 
north  of  Prudence  Park.  They  are  frequently  exposed  (3)  in  almost  all  of 
Bristol  Neck,  north  of  the  granite  area,  only  the  most  western  exposures  on 
the  neck  belonging  to  the  Kingstown  series.  The  shales  form  also  (4)  almost 
the  whole  of  Aquidueck  Island,  excepting  (a)  at  the  top  of  the  syncline  south 
of  Butts  Hill,  and  in  those  areas  occurring  along  (b)  the  southeast  shore  of 
the  island  at  Woods  Castle,  (c)  in  the  Paradise-Purgatory  region,  (rf)  at  the 
Newport  Cliffs,  (e)  on  Miantonomy  Hill,  and  (/)  at  Coddington  Point,  where 
the  overlying  conglomerates  prevail.  The  (g)  pre-CarboniferoiTS  rocks  of 
the  Newport  Neck  region  must  also,  of  course,  be  excluded.  Owing  to  the 
abundant  exposures  of  the  shales  on  Aquidneck  Island  and  the  belief  that 
all  these  shales  form  one  great  series,  the  Aquidneck  exposures  are  considered 
typical,  and  the  shale  series  wherever  exposed  is  therefore  called  the 
Aquidneck  shale  series. 

348 


THE  AQUIDNEOK  SHALES.  349 


SOUTHERN  CONANICUT. 


The  shales  on  Conanicut  form  a  singularl}^  uniform  series.  Owing  to 
abundant  cleavage,  they  are  everywhere  strongly  fissile,  splitting  into  thin 
plates.  The  color  is  usually  dark  blue,  appearing  nearly  black  where 
moistened  by  water,  and  more  brownish  or  greenish  brown  where  very  dry. 
But  variations  from  greenish  to  nearly  black  occur  also,  entirely  aside  from 
any  question  of  moisture,  the  darkening  of  color  being  due  to  the  amount 
of  carbonaceous  material  present.  This  gives  rise  to  an  alternation  of 
darker  and  lighter  color  bands,  which  is  very  characteristic  of  the  shales  in 
many  parts  of  Conanicut,  and  without  which  it  would  rarely  be  possible  to 
determine  the  plane  of  stratification  of  the  rock.  Not  a  trace  of  conglomerate 
or  of  coarse  sandstone  has  so  far  been  found  in  the  shale  series  of  Conanicut. 
Thin  layers  of  a  very  fine-grained  whitish  sandstone  occur  along  the 
southern  margin  of  Dutch  Island  Harbor,  along  the  shore  east  of  Fox  Hill, 
and  on  the  eastern  shore  along  Freebodys  Hill.  Where  there  is  no  color- 
banding  or  whitish  sandstone  there  is  no  means  of  learning  the  real  dip 
and  strike  of  the  shales,  the  cleavage  obscuring  all  traces  of  stratification. 
The  dips  on  the  western  side  of  Conanicut  are  certainly,  in  places,  very 
steep  to  the  westward,  practically  vertical,  but  at  the  first  exposure  south  of 
Fox  Hill  the  dip  is  between  45°  and  60°  E.,  and  this,  in  connection  with 
tlie  general  eastward  dip  of  the  strata  on  Fox  Hill,  is  one  of  the  main 
reasons  for  believing  that  the  Aquidneck  shales  overlie  the  Saunderstown 
sandstones. 

On  the  eastern  side  of  the  western  division  of  the  island — i.  e.,  along 
the  western  side  of  Mackerel  Cove  and  thence  southward — the  dips  are 
usually  eastward  at  angles  which  are  frequently  as  low  as  45°,  and  some- 
times much  lower.  On  the  eastern  side  of  Mackerel  Cove  the  dip  is  low  to 
the  east.  On  Freebodys  Hill  some  of  the  dips  are  nearly  horizontal,  others 
are  low  to  the  east,  and  in  places  the  dip  is  very  variable.  So  little  being 
known  of  the  geological  structure  of  the  island,  it  is  impossible  to  form  a 
close  estimate  of  the  thickness  of  the  shale  series  exposed  there.  A  mini- 
mum estimate  would  be  2,000  feet,  while  4,200  feet  can  not  be  called  a 
maximum  for  the  entire  series,  considering  the  steep  dips  on  the  western 
side  of  the  island.  The  coaly  shales  on  Fox  Hill,  at  Beaver  Head,  may  be 
considered  as  forming  a  transition  series  between  the  Kingstown  sandstones 
beneath  and  the  Aquidneck  shales  above. 


350  GEOLOGY  OF  THE  NAERAGANSETT  BASIN. 


PRUDENCE    ISLAND. 


In  the  case  of  the  coaly  shales  on  the  western  side  of  Prudence  Island, 
it  is  equally  probable  that  these  shales  indicate  the  beginning  of  the  great 
Aquidneck  shale  series  immediately  overlying  them.  On  the  western  side 
of  Prudence  Island  the  Aquidneck  shales  proper  are  of  a  dark-blue  color, 
like  those  on  Conanicut  and  Aquidneck  islands.  The  few  exposures  above 
the  sandstone  series  a  mile  north  of  Prudence  Park  suggest  that  sandstone 
layers  are,  however,  a  more  common  element  in  the  shale  series  here  than  on 
Conanicut.  The  same  observation  also  applies  to  the  exposures  south  and 
southeast  of  Potters  Hotel  (which  is  located  on  the  highest  point  of  the 
island),  where  sandstones  and  even  some  thin  conglomerate  layers  occur. 
Color  banding  is  not  seen  on  the  western  side  of  Prudence  Island,  but  on  the 
eastern  side,  about  two-thirds  of  a  mile  north  of  the  light-house  on  Sand  Point, 
color-banded  shales  like  those  on  Conanicut  are  well  exposed  (PL  XXII). 
South  of  the  light-house  the  shales  are  sericitic,  and  not  so  fissile,  or  at  least 
usually  not  partially  separated  along  the  cleavage  into  thin  plates,  as  they  are 
elsewhere,  yet  it  is  evident  that  these  shales  of  eastern  Prudence  Island  could 
also  be  readily  split  parallel  to  the  cleavage  prodviced  by  the  abundant  pres- 
ence of  this  micaceous  mineral.  An  unusual  feature  is  the  frequent  presence 
south  of  the  light-house  of  sandy  courses,  from  8  to  12  and  even  20  inches 
in  thickness,  some  of  which  merge  into  thin  conglomerate  beds.  One  or  two 
of  the  pebbly  beds  attain  a  thickness  of  2  or  3  feet  and  constitute  a  genuine 
conglomerate.  The  color  of  the  shale  on  this  eastern  side  of  Prudence  Island 
is  more  inclined  toward  the  greenish  hue  of  the  shales  at  Eastons  Point 
than  toward  the  dark  blue  so  common  on  Conanicut  Island.  A  few  more 
carbonaceous  shale  layers  occur  intercalated  among  the  greenish  beds 

The  eastern  Prudence  Island  exposures  south  of  the  hght-house  there- 
fore present  more  frequent  variations  from  the  dark-blue  color  and  tissile 
structure  of  the  Aquidneck  shales,  and  show  more  frequent  sandstone  and 
conglomeratic  layers,  than  do  these  shales  on  southern  Conanicut  or  southern 
Aquidneck.  Sandstones  and  thin  conglomerate  beds  are  fairly  frequent, 
however,  on  Aquidneck  or  Rhode  Island,  directly  east  of  the  Prudence 
Island  exposures  just  described;  also  in  the  area  from  Coggeshall  Point  to 
McCurrys  Point  and  thence  northward  to  within  half  a  mile  of  Butts  Hill. 
These  facts  suggest  an  increase  in  the  amount  of  sandstone,  and  even  the 


THICKNESS  OF  AQUIDNECK  SHALES  OP  PRUDENCE.  351 

introduction  of  cong-lomerate,  in  the  lower  part  of  the  Aquidneck  shales  on 
going  northward. 

THICKNESS    OF    THE    SHALE     SERIES    ON    EACH    SIDE    OP    THE    PBUDBNCE    ISLAND 

SYNCLINE. 

The  structure  of  Prudence  Island  is  a  syncline,  the  sides  dipping  20° 
to  25°  E.  on  the  west  side  (PI.  XXIII),  and  70°  to  80°  W.  on  the  east  side. 
The  bottom  of  the  syncline  appears  to  be  at  Potters  Hotel  or  to  the  west- 
ward. The  thickness  of  shales  forming  the  western  side  of  the  syncline  as 
far  as  exposed  may  be  2,200  feet.  The  thickness  included  in  the  exposures 
forming  the  eastern  side  of  the  syncline  appears  with  more  certainty  to  be 
at  least  1,750  feet.  In  that  case  the  lower  450  feet  exposed  on  the  western 
side  of  the  syncline  may  not  be  exposed  on  the  eastern  side  of  the  island. 
Since  these  estimates  are  not  based  on  a  continuous  series  of  exposures  in 
an  east-west  direction,  there  being  no  exposures  for  almost  a  mile  west  of 
Potters  Hotel,  the  figures  given  can  not  have  great  value,  although  they 
serve  to  give  at  least  some  notion  as  to  the  probable  minimum  thickness  of 
the  shale  formation.  The  sandstones  and  conglomerates  on  the  western 
side  of  Prudence  Island  north  of  the  wharf  being  assigned  to  the  Kingstown 
series,  it  is  evident  that  the  Aquidneck  shale  series  as  exposed  on  this  side 
of  the  island  overlies  the  Kingstown  series.  For  this  reason  the  western 
part  of  the  Prudence  Island  section  is  believed  to  furnish  evidence  in  favor 
of  the  more  recent  age  of  the  Aquidneck  shale  as  compared  with  the  Kings- 
town sandstones.  This  corroborates  the  evidence  furnished  by  the  Beaver 
Head  section  on  Conanicut. 

BRISTOL  NECK. 

The  greenish,  dark-blue,  and  greenish-blue  shales  of  Bristol  Neck  are 
known  to  dip  low  eastward  on  the  western  side  of  the  neck.  If  the  sand- 
stone and  conglomerate  beneath  the  shales  on  the  west  belong  to  the 
Kingstown  sandstones,  the  more  recent  age  of  the  Aquidneck  shales  is 
here  indicated  once  again.  A  sandstone  layer,  becoming  conglomeratic 
near  the  Warren-Bristol  road,  occurs  in  the  shale  series  about  400  feet 
above  the  coarse  conglomerate  layer  at  the  sujjposed  base  of  the  shales, 
and  thus  shows  the  existence  of  occasional  sandy  and  conglomeratic  layers 
in  the  Aquidneck  shale  series  northward.     Sandstone  layers  are  not  known 


352  GEOLOGY  OF  THE  NARRAGANSETT  BASIN, 

to  occur  elsewhere  in  tlie  Aquidneck  shales  of  the  neck.  The  dip  of  the 
stratification  of  the  shales  over  the  middle  and  eastern  part  of  the  neck  can 
not  be  determined  with  certainty.  Under  these  circumstances  there  is  no 
sufficient  evidence  from  which  to  estimate  the  thickness  of  the  Aquidneck 
shales  here  exposed;  1,700  feet  would  appear  to  be  a  very  moderate  esti- 
mate; 2,700  feet  may  be  excessive.  The  low  dips  of  the  sandstone  and 
conglomerate  on  the  western  side  of  Bristol  Neck,  and  the  low  dip  of  the 
coarse  conglomerate  on  the  western  side  of  Warren  Neck,  taken  in  connec- 
tion with  the  small  east-west  extent  of  the  lines  of  exposure  of  the 
Aquidneck  shale  series,  have  caused  the  writer  to  believe  that  the  shale 
series  was  not  so  thick  on  Bristol  Neck  as  it  is  farther  southward,  aiid  that 
probably  the  Aquidneck  shales  diminished  in  thickness  in  passing  northward 
from  southern  Aquidneck  Island  into  Bristol  Neck. 

AQUIDNECK  ISLAND. 

The  Aquidneck  shales  are  typically  exposed  (1)  in  the  Glen  and  (2) 
in  the  valley  south  of  McCurrys  Point  on  the  east  side  of  Aquidneck,  or  the 
Island  of  Rhode  Island;  also  (3)  in  the  valley  east  of  Coggeshall  Point, 
(4)  in  Lawtons  Valley,  and  (5)  in  various  stream  beds,  railway  cuts,  and 
shore  exposures  as  far  south  as  Coddington  Point  and  in  the  railroad  cut 
west  of  Beacon  Hill,  both  on  the  western  side  of  the  island.  The  Aquid- 
neck shales  form  by  far  the  greater  part  of  the  stratified  rocks  of  the  island. 
They  are  characteristically  dark  blue,  and  usually  do  not  show  color  band- 
ing, which  is  also  true  of  the  Bristol  Neck  exposures.  Thin  fine-grained 
sandstone  beds  occur  not  only  in  the  shale  series  northward,  but  also  in 
the  middle  and  southern  part  of  Aquidneck,  where  the  shale  series  is  most 
typically  developed,  so  that  the  Conanicut  shales  are  at  one  extreme  lith- 
ologically  of  the  shale  series,  in  presenting  hardly  any  sandstone  layers  at  all, 
none  of  those  existing  being  even  coarse,  while  the  eastern  Prudence  Island 
and  the  northern  Aquidneck  exposures,  just  east  of  the  Prudence  Island 
exposures,  are  at  the  opposite  extreme,  containing  more  or  less  interbedded 
thin  sandstone  and  some  conglomerate  layers.  On  Aquidneck  Island  thin 
medium-grained  sandstone  beds  occur  in  the  shales  {1)  at  the  north  end  of 
Coddington  Neck  and  (2)  along  the  main  Newport- Bristol  Ferry  road  a  short 
distance  south  of  Lawtons  Valley.  Coarse  sandstone,  merging  in  places 
into  a  very  small-pebbled  conglomerate,  is  found   (3)  east  of  the  railroad 


THICKNESS  OF  SHALES  OF  AQUIDNECK  ISLAND.  353 

half  a  mile  south  of  Lawtons  Valley,  and  a  series  of  exposures  containing 
sandstone  extends  (4)  from  the  valley  east  of  Coggeshall  Point  for  at  least 
half  a  mile  northward.  Sandstone  layers  are  also  exposed  (6)  along  the 
middle  third  of  the  coast  both  on  the  east  and  on  the  west  side  of  the 
island,  and  a  bed  is  also  located  (6)  in  the  lower  part  of  the  Glen  valley. 
Sandstone  occurs  rather  frequently  in  the  shale  series  (7)  for  a  mile  south 
of  Coggeshall  Point,  and  both  sandstone  and  small-pebbled  conglomerate 
layers  occur  (8)  along  the  eastern  shore  from  McCurrys  Point  to  the  expo- 
sures east  of  Butts  Hill. 

THICK:NrESS   OF  THE   SHALE   SECTION  EAST  OF  THE  PORTSMOUTH 

SY]SrCLINE. 

The  geological  structure  of  the  shale  area  over  the  northern  third  of 
Aquidneck  Island  is  evidently  that  of  a  syncline,  the  base  of  the  syncline 
passing  beneath  Butts  Hill  and  extending  a  little  west  of  south  toward  the 
west  of  Quaker  Hill.  The  dip  on  the  eastern  shore  of  the  island  varies 
between  20°  and  40°  W.,  and  at  the  mine  northeast  of  Butts  Hill  it  is 
about  20°  W.  According  to  this  the  coal  seam  opened  at  the  eastern 
coal  mine  could  hardly  be  more  than  500  or  570  feet  above  the  shore 
exposures  along  the  northern  third  of  Aquidneck,  while  the  coarse  con- 
glomerate south  of  Butts  Hill,  and  elsewhere  at  the  same  level  in  the 
syncline,  can  hardly  be  more  than  500  to  650  feet  higher.  According  to 
this  the  shale  section  exposed  on  the  east  side  of  the  syncline  probably 
averages  somewhere  between  1,000  and  1,220  feet,  but  may  be  a  little  less 
than  1,000  feet  in  thickness,  and  might  possibly  exceed  1,300  feet. 

PROBABLE    THICKNESS    OF    THE    SHALE    SECTIOlSr    WEST    OF    THE 
PORTS3IOUTH  SYISTCLIIVE. 

Along  the  shore  north  of  Coggeshall  Point  the  dip  appears  to  be  low 
to  the  east,  usually  not  exceeding  20°.  Farther  east  the  dips  are  steeper  to 
the  east,  varying  most  frequently  between  45°  and  60°  E.  According 
to  this  the  coarse  sandstone  layer  on  the  brow  of  the  hill  east  of  Cogges- 
hall Point  lies  about  1,300  to  1,500  feet  beneath  the  level  of  the  coarse 
conglomerate;  the  shore  exposures  lie  between  1,300  and  1,500  feet  lower 
and  the  western  mine  exposures  occur  apparently  at  a  still  lower  level,  per- 
haps 400  to  500  feet  beneath.     According  to  these  estimates  the  western 

MON  XXXIII 23 


354  GEOLOGY  OF  THE  NAREAGANSETT  BASIF. 

coal  beds  lie  between  3,000  and  3,500  feet  beneath  the  coarse  conglomerate, 
while  the  eastern  bed  lies  between  500  and  570  feet  beneath  the  conglom- 
erate, so  that  eastern  and  western  coal  beds  do  not  belong  to  the  same  hori- 
zon, but  one  imderlies  the  other  about  2,500  to  2,900  feet.  It  should  be 
remembered,  however,  that  these  estimates  ar^  made  without  a  knowl- 
edge of  the  results  obtained  by  a  series  of  diamond-drill  borings  made  west 
of  the  eastern  mine  within  recent  years.  The  apparent  failure  to  detect  on 
the  western  side  of  the  syncline  the  coal  bed  which  was  worked  in  the 
eastern  mine  also  suggests  either  that  the  bed  thins  out  westward  or  that 
it  has  so  far  not  been  discovered  on  that  side  of  the  syncline. 

LITHOIjOGICAr,  VARIATIONS   IK  THE   SHALE   SERIES. 

The  appearance  of  frequent  sandstone  beds  and  an  occasional  con- 
glomerate layer  on  the  eastern  shore,  east  of  the  Portsmouth  s}mcline,  and 
the  exposure  of  only  one  or  two  coarse  sandstone  beds  on  the  western  side 
of  the  syncline,  on  the  brow  of  the  hill  east  of  Ooggeshall  Point  and 
northward  (according  to  preceding  calculations  approximately  at  the  same 
level),  suggests  that  there  may  be  a  reduction  to  the  westward  of  the 
amount  of  sandy  material  at  this  particular  horizon.  In  a  general  way 
also  there  appears  to  be  more  carbonaceous  material  in  the  shale  series  on 
the  east  side  of  the  Island  of  Aquidneck  than  at  corresponding  heights 
westward,  and  there  is  certainly  less  carbonaceous  material  in  the  shale  on 
Prudence  Island  and  on  Bristol  Neck  than  eastward.  Observations  of  this 
nature  have  little  value,  however,  since  the  recorded  strikes  and  dips  are 
not  sufficient  in  number  to  give  assurance  regarding  the  strike  and  dip  of 
the  intermediate  localities,  where  exposures  fail  or  where  the  stratification 
has  been  obscin-ed  by  cleavage. 

GEOLOGICAL   STRUCTURE   OF  THE  MIDDLE  THIRD   OF  AQUIDNECK 

ISLAND. 

From  McCurrys  Point  to  the  exposures  half  a  mile  north  of  Black 
Point,  little  can  be  determined  about  the  dip  of  the  rocks.  In  the  Glen  a 
sandstone  layer  appears  to  be  nearly  horizontal.  Nothing  satisfactory  could 
be  determined  about  the  dip  of  the  exposures  along  the  road  from  Slate 
Hill  south  westward.     North  and  south  of  Lawtons  Valley,  and  at  several 


STEUCTURE  OF  AQUIDNEOK  SHALES.  355 

points  along  the  western  shore,  the  dip,  however,  is  distinctly  eastward. 
Over  this  more  eastern  part  of  the  middle  third  of  Aquidneck  Island  the 
strata  are  beheved  to  be  inclined  at  a  low  angle,  and  to  form  a  series  of 
low  folds,  leaving  the  rocks  in  general  essentially  horizontal.  Along  the 
western  coast,  however,  and  for  a  distance  of  a  mile  or  more  east  of  the  same, 
more  marked  eastward  dips  occasionally  occnr,  and  here  the  folding  may 
be  more  pronounced,  although  the  recorded  observations  so  far  fail  to  give 
evidence  of  marked  folding. 

STRATA  PROBABLY  FOLDED. 

If  the  coarse  conglomerates  of  Coddington  Point,  Coasters  Harbor 
Island,  and  Miantonomy  Hill  correspond  to  the  coarse  conglomerates  in  the 
northern  third  of  the  island,  it  is  evident  that,  in  spite  of  the  eastward  dips 
so  far  recorded  from  the  western  Portsmouth  mine  as  far  as  Coddington 
Point,  there  must  be  some  system  of  folding  as  yet  not  discovered,  which 
(1)  allows  the  Miantonomy  Hill  exposure  of  conglomerate  to  appear  to  the 
west  of  the  line  of  strikes  shown  by  the  shales  to  the  northward,  while  they 
are  still  evidently  above  the  Aquidneck  shales  as  exposed  near  the  hill;  (2) 
the  fact  that  the  Coasters  Harbor  Island  and  the  Coddington  Point  expo- 
sures of  coarse  conglomerate  lie  at  least  1 00  feet  beneath  those  at  Mianton- 
omy Hill  suggests  that  there  must  be  folding  between  these  localities,  if 
the  two  sets  of  coarse  conglomerates  are  to  be  considered  as  of  the  same 
age,  and  the  exposures  at  Coasters  Harbor  Island  and  Miantonomy  Hill 
favor  that  view. 

The  synclinal  structure  of  the  southern  half  of  Prudence  Island  and 
the  northern  third  of  Aquidneck  Island  demands  anticlinal  structure  in  the 
region  between.  How  far  south  either  the  anticline  along  the  Eastern 
Passage  or  the  syncline  of  Prudence  Island  extended  is  unknown.  Are  the 
coal  beds  in  the  western  mines  near  the  base  of  the  Aquidneck  shale  series? 
Do  these  coals  thin  out  westward!  Are  the  coaly  shales  on  the  western 
shore  of  Prudence  Island  the  representatives,  in  a  general  way,  of  the 
thicker  coal  beds  at  the  Portsmouth  mine!  Do  the  coaly  shales  of  Gould 
Island  belong  to  the  same  horizon — i.  e.,  that  of  the  Portsmouth  mine  coal 
beds!  These  are  questions  which  can  not  be  satisfactorily  answered  in  the 
present  state  of  our  knowledge. 


356  GEOLOGY  OF  THE  NAEEAGANSETT  BASIN. 

GOULD   ISLA>^D   or   THE   3IIDDLE   PASSAGE. 

The  strike  of  the  strata  composing  Gould  Island  is  generally  north- 
south.  Plumbago  and  coaty  shales  form  almost  all  of  the  shore  exposm'es 
on  the  eastern  shore  for  a  little  more  than  half  the  length  of  the  island, 
going  southward.  Farther  south  carbonaceous  shales  continue  to  appear, 
but  sandstone,  in  part  conglomeratic,  also  makes  its  appearance.  The  peb- 
bles of  the  more  conglomeratic  layers  are  very  small.  The  dips  are  chiefly 
east,  but  very  irregular,  and  the  most  northern  dip  appears  to  be  westward, 
while  the  strata  about  a  fourth  of  the  length  of  the  island  north  of  its 
southern  end  are  nearly  vertical. 

SOLTTHERIS^   THIRD    OF   AQLIDKECK    ISEAIN^D. 

South  of  the  line  connecting  Coddington  Point  and  Black  Point,  includ- 
ing the  southern  third  of  Aquidneck  Island,  the  t3'pical  dark-blue  and 
greenish-blue  shales  of  the  Aquidneck  series  are  not  often  exposed  (see  foot- 
note on  page  372).  The  top  of  the  series  is  exposed  at  Eastons  Point,  but 
presents  features  which  it  is  desirable  to  discuss  in  connection  with  other 
exposures  farther  north  that  seem  to  belong  to  the  same  horizon.  This  will 
be  done  under  the  next  heading. 

UPPER  GREEX  SHAEES  OF  THE  AQUIDXECK  SERIES. 

The  great  mass  of  shales  exposed  on  Aquidneck  or  Rhode  Island 
undoubtedly  constitute  a  single  series.  Considering  their  thickness  and 
their  considerable  geographical  distribution,  they  present  decided  litho- 
logical  uniformity.  Along  the  middle  of  Aquidneck  Island,  however,  the 
upper  part  of  the  shale  is  greenish  in  color,  in  contrast  to  the  chiefly  dark- 
blue  fissile  shales  underneath.  These  green  shales  are  well  exposed  (1) 
for  a  mile  along  the  western  road  from  Newport  to  Bristol  Ferry,  south- 
west of  Butts  Hill,  on  the  western  side  of  the  Portsmouth  syncline.  They 
are  seen  again  (2)  half  a  mile  southwest  of  the  top  of  Quaker  Hill,  on  the 
eastern  side  of  the  syncline.  The  green  shales  include  near  the  top  more 
sandy  layers  and  sandstones,  followed  liigher  up  by  the  sandstones  and 
conglomerates  of  the  conglomerate  series.  At  (3)  Slate  Hill  and  for  over 
a  mile  southwestward  along  the  road  green  shales  are  again  exposed.  The 
coarse  conglomerate  series  which  is  supposed  once  to  have  overlain  them  is 


SANDSTONES  WEST  OF  SAKONNET  EIVEE.  357 

no  longer  present,  and  if  ever  in  existence  here  must  have  been  removed 
by  erosion.  At  (4)  Eastons  Point  greenish  shales  verging  to  bluish  are  well 
exposed  beneath  the  coarse  conglomerate  on  both  sides  of  the  anticline. 
The  greenish  shales  of  all  these  localities  are  believed  to  represent  the  top 
of  the  great  Aquidneck  shale  series.  This  does  not  mean  that  all  of  the 
greenish  shales  elsewhere  also  belong  to  this  upper  horizon.  The  greenish 
shale  of  the  western  part  of  Bristol  Neck  certainly  belongs  low  in  the  shale 
series,  and  not  at  the  top,  but  along  the  middle  length  of  Aquidneck  Island, 
from  the  Portsmouth  syncline  to  Eastons  Point,  such  a  north-south  line  of 
green  shales  near  the  top  of  the  Aquidneck  shales  can  be  recognized. 

SAKONNET  SAISTDSTONES   OF   THE  AQUIDNECK   SERIES   WEST  OF   THE 

RIVEK. 

West  of  the  Hue  of  upper  green  shales  just  described  the  corresponding 
upper  layers  of  the  Aquidneck  shale  series  are  not  greenish  in  color,  but  show 
the  more  usual  dark-blue  tinge.  This  is  certainly  true  beneath  the  Mian- 
tonomy  Hill  and  Coddington  Point  conglomerates,  where  the  underhung 
shales  seem  to  represent  the  same  horizon.  Eastward  of  the  line  of  upper 
green  shales  described  there  are  other  exposures  of  the  upper  shales  of  the 
Aquidneck  series,  which  are  also  occasionally  green  in  color — for  instance, 
north  of  the  conglomerate  area  at  Fogland  Point.  But  usually  the  more 
eastern  exposures  of  the  upper  Aquidneck  series  fail  to  show  a  marked 
shaly  character;  on  the  contrary,  they  more  frequently  become  more 
sandy  in  some  of  their  layers,  or  even  take  on  the  general  character  of  a 
sandstone  series,  in  which  shales  form  only  the  subsidiary  beds.  When  this 
occurs,  the  finer  sandstones  usually  contain  considerable  carbonaceous 
material.  Such  shales  with  a  predominating  amount  of  dark-gray  or 
blackish  sandstones  are  found  at  the  top  of  the  Aquidneck  shale  series  and 
beneath  the  coarse  conglomerates  along  the  shore  north  of  Black  Point, 
and  to  a  less  pronounced  degree  at  Taggarts  Ferry.  The  more  sandy 
character  of  the  upper  part  of  the  Aquidneck  series  along  the  southeastern 
side  of  the  island  may  indicate  approach  to  shore  conditions  in  that  direction. 

THICKlSrESS  OF  THE  UPPER  GREEN  SHAEES. 

The  thickness  of  the  upper  green  shales  on  the  western  side  of  tlie 
Portsmouth  syncline  is  probably  at  least  150  feet,  and  this  is  certainly  the 
smallest  possible  estimate  for  the  thickness  of  the  green  shale  series  exposed 


358  GEOLOGY   OF  THE  NAERAGANSETT  BASIK 

at  Slate  Hill  and  southwestwarcl.  The  exposed  portion  of  the  shales 
beneath  the  conglomerates  at  Eastons  Point  adds  up,  according  to  Prof. 
T.  Nelson  Dale,  to  at  least  600  feet,  with  an  unknown  thickness  of  shales 
beneath,  but  even  the  shales  exposed  can  not  all  be  called  green.  The 
thickness  of  the  upper  green  shales  must  occasionally  equal  200  to  250  feet. 

THICKNESS  or  THE  SAKOjSTSIET  SANDSTONES. 

The  upper  sandstones  and  shales  beneath  the  conglomerates  at  Black 
Point  have  a  thickness  of  at  least  110  feet,  while  their  total  thickness  at  this 
point  is  evidently  greater.  The  corresponding  series  at  Taggarts  Ferry 
can,  however,  hardly  exceed  that  amount.  Their  thickness  east  of  the  river 
is  discussed  later. 

The  thickness  of  the  more  typical  dark-blue  Aquidneck  shales  probably 
exceeds  3,000  feet.  The  upper  green  shales  and  the  Sakonnet  sandstones 
do  not  add  considerably  to  this  thickness,  so  that  an  estimate  of  3,000  to 
3,500  feet  for  the  Aquidneck  shale  series  seems  reasonable^  Desirable  as  it 
would  be  to  secure  a  better  idea  of  the  total  thickness  of  the  Aquidneck 
s|iales,  this  is  at  present  impossible.  The  accessible  data  do  not  furnish  the 
means  for  such  an  estimate. 

NOETHEEN  EXTENSION  OF  THE  AQUIDNT:CK  SHAEES. 

North  of  Bristol  Neck  the  Aquidneck  shale  series  seems  to  lose  its 
identity.  Greenish-blue  shales  continue  to  be  exposed  at  several  points  a 
mile  north  of  the  Warren  and  Fall  River  Railroad,  but  on  continuing  north- 
ward are  soon  intercalated  with  sandstones  and  conglomerates  to  such  an 
extent  that  they  can  no  longer  be  recognized  as  a  distinct  series,  but 
evidently  merge  northward  into  the  upper  part  of  Mr.  Woodworth's  lower 
Coal  Measures  series. 

EQUIVALENTS    OF    THE    KINGSTOWN    SANDSTONTE    AND    AQUIDNECK 
SHALE   SEEIES  NOETHEAST   OF  WAEEEN  NECK. 

East  of  Aquidneck  Island  and  Bristol  and  Warren  necks  it  appears 
impossible  to  distinguish  between  a  lower  Kingstown  sandstone  and  an 
upper  Aquidneck  shale  series.  Sandstones  and  shales  are  exposed  below 
the  coarse  conglomerates  southwest  of  Swansea  village.     Coaly  shales  are 


SANDSTONES  EAST  OF  SAKONNET  RIVER.  359 

found  five-eigliths  of  a  mile  north  of  South  Swansea  Station.  Shaly  sand- 
stones occur  west  of  Lees  River  north  of  the  raih-oad.  At  Bi-aytons  Point 
very  coaly  shales  and  some  sandstones  are  exposed.  Northeastward,  on 
Sewammock  Neck,  sandstone  is  found.  The  exposures  east  of  Taunton 
River  inchide  the  arkoses  resting  upon  pre-Carboniferous  granites,  both  of 
which  will  be  discussed  later. 

The  section  included  between  the  coarse  conglomerate  of  Swansea  vil- 
lage and  the  arkoses  of  Steep  Brook  or  Fall  River  must  correspond  in  some 
measure  to  the  Aquidneck  shales  and  possibly  to  more  or  less  of  the  Kings- 
town sandstones  as  described  from  the  main  area  of  the  basin  toward  the 
southwest.  If  the  section  from  Swansea  village  to  Steep  Brook  be  consid- 
ered as  simple  in  geological  structure,  tolerably  free  from  local  folding 
or  marked  changes  of  dip,  a  supposition  by  no  means  certain,  fair  esti- 
mates might  be  made  as  to  its  thickness.  If  the  strata  be  supposed  to  be 
inclined  toward  the  northwest  at  an  average  angle  of  45°,  a  thickness  of 
10,600  feet  would  have  approximate  value,  while  at  an  inclination  of  60° 
the  thickness  of  section  might  equal  13,800  feet.  The  thickness  of  the 
Kingstown  sandstones  was  placed  above  at  11,500  feet,  and  that  of  the 
Aquidneck  shales  at  3,000  to  3,500  feet,  making  a  total  thickness  of  14,500 
to  15,000  feet  for  the  corresponding  strata  farther  southwest.  Unfortunately 
all  these  estimates  are  based  on  data  either  not  strictly  reliable  or  even  not 
fairly  satisfactory,  especially  since  in  the  regions  where  the  estimates  are 
made  there  are  areas  where  exposures  are  few,  but  these  estimates  are  at 
least  the  best  at  present  available.  While  it  is  impossible  to  distinguish  an 
upper  Aquidneck  shale  from  a  lower  sandstone  series  between  Swansea 
village  and  Steep  Brook,  yet  the  existence  of  abundant  shales  in  the  upper 
part  of  this  section  should  be  distinctly  recognized  as  an  approach  to  the 
lithological  distinctions  in  existence  farther  southwestward. 

SAKOKXET  SAKDSTOlSrES   OX  THE  EAST  SIDE  OF  THE  RIVER. 

That  the  upper  part  of  the  Aquidneck  shales,  that  portion  immediately 
underlying  the  coarse  conglomerate  series,  loses  its  shaly  character  and 
assumes  more  of  a  sandstone  nature  eastward  has  already  been  noted  in 
speaking  of  the  exposures  north  of  Black  Point  and  at  Taggarts  Ferry,  on 
the  southeastern  shore  of  Aquidneck  Island.  On  the  eastern  side  of  the 
Sakonnet  River,  east  of  Aquidneck  Island,  the  rocks  underlying  the  coarse 


360  GEOLOGY  OF  THE  NAERAGANSETT  BASIN. 

conglomerate  series  consist  also  chiefly  of  sandstone.  Some  of  the  sand- 
stone layers  contain  scattered  pebbles,  or  even  thin  streaks  of  conglomerate; 
conglomerates  with  pebbles  of  moderate  size  also  occur,  but  do  not  consti- 
tute an  important  element  of  the  Sakonnet  sandstones.  Shaly  layers  are 
more  common,  and  occasionally  attain  considerable  thickness — for  instance, 
in  the  case  of  the  coaly  shales  along  the  shore  directly  west  of  Windmill 
Hill.  As  a  rule,  however,  the  sandstones  predominate  very  miich  at  this 
horizon.  The  sandstone  exposures  north  of  High  Hill,  and  the  sandstone, 
shale,  and  fine  conglomerate  extending  from  the  shore  west  of  Windmill 
Hill  nearly  to  Browns  Point,  are  characteristic  exposures  of  this  Sakonnet 
sandstone  on  the  east  side  of  the  river.  The  shales  and  sandstones  south 
of  Corys  Wharf  may  possibly  represent  some  lower  horizon  in  the  Aquid- 
neck  shale  series. 

ABSENCE   OP   THE   SHALE  SERIES   BENEATH    THE    COABSE   CONGLOM- 
EEATES   EAST  OF  THE   SAKONNET  RIVER. 

The  upper  Aquidneck  shales  are  therefore  believed  to  merge  into 
sandstones  on  approaching  the  present  eastern  border  of  the  Carboniferous 
basin.  And  this  may  be  true  also  of  the  lower  horizons  of  this  series.  If 
the  coarse  conglomerates  on  the  eastern  side  of  the  Sakonnet  River  be, 
indeed,  the  equivalents  of  the  coarse  conglomerates  on  Aquidneck  Island  and 
northwest  of  Taunton  River,  and  if  the  sandstones  just  mentioned  belong 
to  the  Sakonnet  series  as  interpreted  west  of  the  river,  very  little  space 
intervenes  in  most  localities  on  the  east  side  of  the  Sakonnet  River  between 
these  conglomerates  and  sandstones  and  the  basal  arkose  layers  and  coaly 
shales.  The  section  east  of  the  Sakonnet  River  must  have  had  a  somewhat 
different  historj?-  from  that  on  the  mainland  west  of  the  bay.  An  extensive 
system  of  irregular  faulting  would  seem  to  oifer  a  possible  explanation  for 
this  sudden  diminution  of  the  Aquidneck  shale  and  Kingstown  sandstone 
section.  The  irregularity  of  the  dip  and  strike  of  the  coarse  conglomerate 
exposures  and  .their  areal  distribution  would  seem  to  favor  the  existence  of 
marked  local  faulting.  But  it  is  also  possible  that  the  basal  arkose  east  of 
the  bay  is  not  identical  in  age  with  that  west  of  the  bay.  It  may  belong 
to  a  higher  horizon,  possibly  corresponding  to  part  of  the  Aquidneck  shale 
series.  In  that  case  the  failure  of  any  equivalent  of  the  Kingstown  sand- 
stone series  to  appear  east  of  the  bay  is  not  so  surprising. 


DISTRIBUTION  OF  AQUIDNECK  SHALES.  361 

WEDGE-SHAPED   AREAL    DISTRIBUTION   OF   THE    AQUID^TECK  SHAEE 

SERIES. 

If  the  King-stowu  series  may  be  compared  with  a  wedge  tapering 
southward,  the  Aquidneck  shales  may  be  said  to  form  a  wedge-shaped  area 
tapering  northward,  at  least  as  far  as  Bristol  Neck.  From  the  northern  end 
of  this  wedge-shaped  mass  a  narrower  area  extends  northeastward  toward 
Taunton  River.  This  wedge-shaped  areal  distribution  suggests  a  general 
inclination  of  the  southern  part  of  the  Carboniferous  formation  toward  the 
south-southeast,  a  feature  possibly  to  be  studied  in  correlation  with  the  south- 
ward pitch  of  the  rocks  involved  in  the  various  coarse  conglomerate  synclines 
and  anticlines  found  in  the  southern  third  of  Aquidneck  Island.  The  pecu- 
liar combination  of  northeast  with  more  northerly  boundary  lines  between 
the  sandstone  and  the  shale  series  finds  expression  elsewhere  in  the  sudden 
changes  in  the  direction  of  the  shore  line  on  the  various  islands,  in  the  strikes 
of  the  chief  cleavage  planes,  and,  to  a  certain  extent,  in  the  trends  of  the 
hills.  These  facts  suggest  that  the  Carboniferous  series  has  been  subjected 
to  two  systems  of  folding,  making  moderate  angles  with  each  other,  the  one 
causing  folds  trending  more  nearly  north-south  and  the  other  east  of  north. 

EQUIVAEE:tirCE   OF  THE  KINGSTOWK  SANDSTONES   AND   THE   AQUID- 
NECK SHAEES. 

A  reference  to  the  map  will  show  that  the  identifiable  Kingstown 
sandstones  are  confined  to  the  western  side  of  the  Narragansett  Basin,  while 
the  Aquidneck  shales  belong  to  the  middle  area,  so  that  the  Kingstown 
sandstones  border  in  a  general  w&j  the  Western  Passage  of  the  bay,  while 
the  Aquidneck  shales  border  the  Eastern  Passage  and  a  pai-t-  of  the  Sakon- 
net  River.  It  has  therefore  several  times  been  a  serious  question  whether 
these  two  formations  may  not  be  equivalent,  the  western  Kingstown  sand- 
stone and  shale  series  passing  toward  the  east  into  a  typically  more  shaly 
Aquidneck  phase.  An  interpretation  of  this  kind  would  much  simplify  the 
conception  of  the  geology  of  the  southern  part  of  the  Narragansett  Basin. 
Unfortunately  there  are  insuperable  difficulties  of  observation  at  the  very 
point  where  the  transition  between  these  two  formations  should  be  traced. 
The  exposures  along  the  Bonnet,  those  on  Dutch  Island,  which  do  not  lie 
far  above  the  same,  and  the  rocks  along  the  western  shore  of  northern 
Conanicut,  along  Slocums  and  Great  ledges,  all  e\ddently  belong  to  the 
Kingstown  series,  while  the  shales  on  southern  Conanicut,  from  Beaver 


362  GEOLO&Y  OF  THE  NARRAGANSETT  BASIjST. 

Tail  to  Mackerel  Cove  and  Dutch  Island  Harbor,  probably  even  as  far  as 
Potters  Cove,  north  of  Freebod}^  Hill,  belong  to  the  Aquidneck  shales.  At 
the  former  localities,  sandstones  and  even  small-pebbled  conglomerates  are 
fairly  common,  while  at  the  latter  conglomerates  and  coarse-grained  sand- 
stones are  altogether  unknown,  and  sandstones  of  any  description  are 
exceedingly  rare.  Nothing  could  be  in  greater  contrast  than  the  exposures 
on  Fox  Hill  and  those  on  the  main  body  of  Conanicut  from  Freebody  Hill 
to  Beaver  Tail.  There  is  no  transition  between  the  Kingstown  series  and 
the  Conanicut  shales  in  this  region.  The  dissimilarity  here  is  indeed  far 
greater  than  farther  northeast,  where  the  Aquidneck  shales  contain  more  or 
less  sandstone.  Sandstones  and  even  a  little  conglomerate  occur,  for 
instance,  in  the  Aquidneck  shales  of  Prudence  Island,  and  in  the  shales  on 
Aquidneck  itself,  especially  near  the  base  of  the  formation.  Sandstones 
form  a  few  widely  distant  beds  also  at  higher  altitudes  in  the  shale  series 
on  Aquidneck  Island,  but  sandstones  are  not  common  in  the  upper  beds 
until  the  Sakonnet  sandstones  are  reached.  However,  neither  on  Prudence 
Island  nor  on  Aquidneck  Island  is  it  possible  to  recognize  a  transition, 
either  lateral  or  vertical,  from  the  Kingstown  into  the  Aquidneck  series. 

The  Aquidneck  shale  series  is  therefore  most  distinct  from  the  Kings- 
town sandstone  in  the  areas  where  the  two  series  are  most  typically 
developed — at  the  nearest  point  of  approach  of  these  areas,  at  Fox  Hill  on 
Conanicut  Island;  and  on  the  western  side  of  Prudence  Island  the  dips 
indicate  that  the  Aquidneck  shales  overlie  the  Kingstown  sandstones,  and 
for  the  present  the  conclusion  must  be  that  the  shales  overlie  the  sandstone- 
shale  series,  and  this  has  been  the  interpretation  in  this  monograph. 

This  does  not,  however,  overlook  the  facts  that  the  shale  series  on 
Prudence  Island  msij  contain  rather  frequent  sandstone  and  some  con- 
glomerate beds,  that  on  Aqiiidneck  Island  they  may  contain  many  sand- 
stone beds  near  the  base  and  a  few  higher,  and  that  in  Cranston,  East 
Providence,  Swansea,  and  northward  they  contain  so  much  sandstone,  and 
even  conglomerate,  that  the  two  formations  can  no  longer  be  distinguished, 
but  are  merged  into  a  general  Carboniferous  series  of  shales,  sandstones, 
and  to  some  extent  conglomerates. 

The  distinction  between  Kingstown  sandstones  and  Aquidneck  shales 
therefore  disappears  in  the  northern  part  of  the  area  comprised  in  the 
bay  region  of  the  Narragansett  Basin,  but  the  difference  between  these 


rv  '^"  ' -    .   ■' ■ 

'•■ 

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; 

i^u^ 


'       '   "       ^'■- 


FOSSILS  OF  AQUIDNECK  SHALES.  363 

formations  farther  south  is  sufficiently  marked  to  warrant  their  separation 
in  this  part  of  the  report. 

It  is  not  impossible  that  the  Kingstown  series  is  not  at  all  exposed  east 
of  the  Eastern  Passag-e.  The  section  between  the  coarse  conglomerates 
and  the  basal  ai'koses  is  evidently  much  smaller  there  than  on  the  western 
side  of  the  bay,  and  no  exposures  assignable  to  the  Kingstown  series  are  in 
direct  evidence. 

The  Aquidneck  shales  on  the  southwestern  margin  of  Prudence  Island 
have  weathered  in  an  irregular  manner,  producing  many  small  cavities 
upon  the  surface  of  the  shales,  giving  the  appearance  of  irregular  fretwork 
(PL  XXIV). 

FOSSILS   OF  THE   AQITIDNECK   SHALE  SERIES. 

Fossils  are  found  in  the  Aquidneck  shales  at  various  horizons.  The 
fossiliferous  horizon  at  their  very  base  has  already  been  mentioned — for 
instance,  in  the  case  of  the  coaly  shale  on  the  western  shore  of  southern 
Prudence  Island.  The  western  Portsmouth  mine  exposures  of  northern 
Aquidneck  possibly  represent  a  somewhat  higher  horizon,  fern  impressions, 
calamites,  and  Sigillai'ia  occurring  there.  Next  comes  the  fern  locality  near 
the  termination  of  Corys  Lane,  on  the  western  shore  of  the  island;  then 
the  locality  just  east  of  the  railroad  in  the  gnlly  half  a  mile  north  of  Law- 
tons  Valley,  where  a  few  ferns  were  found;  next,  a  mile  southeast  of  Carrs 
Point,  on  the  western  Newport- Bristol  Ferr)^  road.  The  fern  impressions 
found  half  a  mile  south  of  the  wharf  on  the  eastern  Portsmouth  shore,  and 
those  found  a  short  distance  north  of  the  Glen,  may  belong  to  about  the 
same  horizon.  The  fern  impressions  found  along  the  roadside  tlii-ee-fourths 
of  a  mile  northeast  of  Butts  Hill  probably  represent  a  higher  horizon. 
Those  at  the  northern  side  of  the  Old  Fort,  on  the  side  north  of  Butts  Hill, 
are  still  higher  in  the  series.  If  the  conglomerates  at  Coddington  Point 
belong  to  the  group  of  coarse  conglomerates  overlying  the  Aquidneck 
shales,  the  fern  impressions  near  the  northern  end  of  the  point  represent  a 
horizon  above  their  base.  The  fern  locality  along  the  coast  a  mile  and  a  half 
north  of  Coddington  Point  at  present  can  not  be  well  located  stratigraph- 
ically.  The  same  statement  applies  with  greater  force  to  the  fern  locality 
on  the  western  side  of  Braytons  Point,  which  consists  of  coaly  shales,  such 
as  exist  near  the  top  of  the  sandstone  series  in  the  more  western  parts  of  the 
bay  region,  but  the  jjrecise  stratigraphic  position  of  the  deposit  is  unknown. 


CHAPTEE  IX. 

THE  PURGATORY  CONGLOMERATE. 

Coarse  conglomerate  overlying  the  Aquidneck  shale  series. TllG    KuigStOWn   Sei'ieS  IS   OVei'- 

lain  by  a  considerable  thickness  of  sliales,  here  termed  the  Aquidneck 
series.  These  shales  retain  their  shaly  characteristics  and  bluish-black  color 
to  within  a  very  short  distance  of  the  base  of  the  overlying  coarse  conglom- 
erate at  Coasters  Harbor  Island,  Coddington  Point,  and  Miantonomy  Hill. 

Farther  eastward,  near  the  top  of  the  Portsmouth  syncline,  at  Slate 
Hill  and  southwestward,  and  to  a  less  degree  on  both  sides  of  the  Eastons 
Point  anticline,  the  upper  portion  of  the  shale  series  has  a  more  greenish 
color,  and  at  the  first  and  last  mentioned  localities  this  upper  greenish  shale 
evidently  lies  immediately  under  the  coarse  conglomerate  of  these  regions; 

At  Taggarts  Ferry  the  bluish  Aquidneck  shales  are  exposed  in  the 
stream  bed  entering  the  bay  from  the  west,  within  a  very  short  distance 
from  the  shore.  Overlying  these  shales  is  a  variable  series  composed  of 
bluish  shales,  carbonaceous  shales,  black  fine-grained  sandstones,  less  car- 
bonaceous and  coarser-grained  sandstones,  and  conglomerates  with  the 
pebbles  usually  small.  These  occur  in  alternating  beds,  and  have  ah-eady 
been  described  under  the  name  of  Sakonnet  sandstones.  Immediately  over- 
lying them  is  coarse  conglomerate. 

The  dark-blue  Aquidneck  shales  are  well  exposed  at  the  Glen.  South- 
ward along  the  shore  the  shales  are  usually  more  black  and  carbonaceous. 
Just  before  reaching  Black  Point  an  overlying  series  of  dark  shales,  dark 
carbonaceous  fine-grained  sandstones,  and  very  small-pebbled  conglomerate 
comes  in,  representing  a  more  northern  variety  of  the  Sakonnet  sandstones. 
Overlying  these  sandstones  is  the  same  coarse  conglomerate  which  was 
mentioned  in  describing  the  exposures  at  Taggarts  Ferry. 

East  of  the  Sakonnet  River  there  are  no  exposures  of  the  typical 
Aquidneck  shale  variety,  but  the  coarse  conglomerates  occur,  and  immedi- 
ately beneath  the  latter,  according  to  this  interpretation  of  the  geological 

364 


POSITION  OF  SAKONNET  SANDSTONES.  365 

structure  of  this  region,  occur  the  shale,  sandstone,  and  fine  conglomerate 
beds,  forming  the  Sakonnet  sandstones  east  of  the  river,  from  the  shore 
west  of  Windmill  Hill  almost  as  far  as  Browns  Point.  The  thickness  of  the 
sandstones  along  this  part  of  the  shore  must  amount  to  at  least  300  feet, 
but  no  accurate  measurements  were  obtained. 

Underlying  the  coarse  conglomerate  of  High  Hill  Point  is  more  sand- 
stone and  small-pebbled  conglomerate.  Immediately  beneath  the  Fogland 
Point  conglomerate  is  greenish  shale.  The  exposures  south  of  Corys 
Wharf,  consisting  of  bluish  shale  with  some  sandstone,  approach  more 
nearly  to  some  of  the  Aquidneck  exposures  west  of  the  Sakonnet  River 
than  any  other  exposures  known  on  the  eastern  side  of  the  bay.  They 
undotibtedly  belong  beneath  the  coarse  conglomerate,  and  lie  at  about  the 
same  horizon  as  some  of  the  Sakonnet  sandstones  farther  southward. 

Sakonnet    sandstones  within   the  Aquidneck    shales,   in  transition   to    the   coarse   conglomerate. 1  lie 

Sakonnet  sandstones  are  here  placed  with  the  Aquidneck  shales,  owing  to 
the  frequent  intercalation  of  shales,  and  because  the  dividing  line  is  more 
readily  drawn  above  than  below  the  sandstones.  At  the  same  time  these 
sandstones,  with  the  interbedded  small-pebbled  conglomerate  layers,  are 
undoubtedly  introductory  to  the  coarse  conglomerate  series  above. 

Coarse    conglomerate    forming  the   latest   Carboniferous    rocks    in   the   southern   part  of  the   Narragansett 

Basin. — The  various  coarse  conglomerate  exposures  mentioned  form  the 
summit  of  the  rocks  of  Carboniferous  age  in  the  localities  where  they  are 
found.  Under  these  circumstances  the  temptation  is  very  great  to  consider 
them  all  as  being  of  the  same  general  horizon. 

Purgatory  conglomerate  as  a  typical  exposure. TllC   pOSitioU    of   tllC    COarSC    COUgloUl- 

erate  at  Eastons  Point  is  perhaps  the  best  defined.  It  occurs  on  both  sides 
of  the  anticline  forming  the  point,  and  the  exposures  on  the  eastern  side  of 
the  anticline  containing  the  famous  Purgatory  chasm  can  be  readily  traced 
northward  to  the  high  conglomerate  ridges  forming  the  western  side  of  the 
Paradise  region  northwest  of  the  reservoir.  The  southward  pitch  of  this 
anticline  is  the  best  assurance  that  this  coarse  conglomerate  occupies  a 
higher  position  than  shales  of  the  Aquidneck  series. 

The  upper  green  shales  occur  on  Slate  Hill  at  an  elevation  of  260  feet 
About  a  mile  southward  they  occur  at  a  level  of  180  feet.  At  Eastons 
Point  a  restoration  of  the  syncline  would  probably  give  a  somewhat  lower 
elevation  to  that  part  of  the  section  which  most  nearly  corresponds  to  the 


366  GEOLOGY  OF  THE  NAREAGANSETT  BASIN. 

greenish  shales  northward.     This  apparently  coi-roborates  the  e%'idence  in 
favor  of  a  general  southward  pitch  of  the  rocks  in  southern  Aquidneck. 

Owino-  to  the  typical  development  of  the  coarse  conglomerate  series  at 
Purgatory,  and  its  already  well-known  occurrence  as  shown  by  frequent 
references  in  geological  hterature,  the  name  Purgatory  conglomerate  is  chosen 
to  designate  those  coarse  conglomerates  which  are  supposed  to  belong  to 
the  same  hoi-izon. 

Identity  of  the  Purgatory  and  the  Sakonnet  River  western  shore  coarse  conglomerate i  here  COUid 

be  no  closer  lithological  resemblance  than  that  between  the  conglomer- 
ates exposed  between  Black  Point  and  Smiths  Beach  along  the  Sakonnet 
River  or  East  Passage  and  the  similar  beds  in  the  Purgatory  and  western 
Paradise  regions.  The  lithological  character  of  the  slaty  and  quartzose 
pebbles,  the  inclosed  oboli,*  the  great  size  of  the  pebbles,  the  alternation 
of  the  coarse  conglomerates  with  sandstones,  the  same  varieties  of  medium- 
grained  granite  pebbles  and  the  same  infrequency  of  granite  as  compared 
with  quartzitic  pebbles,  and  many  other  points  easily  recognized  in  the 
field,  all  suggest  the  identity  of  the  two  series.  The  presence  of  Aquidneck 
shales  in  the  region  northwest  of  Black  Point  and  the  eastward  dip  of  the 
coarse  conglomerate  suggest  superposition  of  the  coarse  conglomerate  upon 
the  Aquidneck  shales. 

Possible   syncline  between  the  two  western   Paradise  ridges  of  conglomerate. i  lie      r  UrgatOry 

and  western  Paradise  exposures  and  the  Sakonnet  River  western  shore 
exposures  just  mentioned  dip  eastward.  In  order  to  place  them  at  the  same 
horizon,  it  seems  necessary  to  imagine  at  least  one  syncline  somewhere 
between  the  two  lines  of  exposure.  The  main  ridge  of  the  Paradise  region, 
forming  its  western  boundary,  e^ddently  dips  eastward,  most  of  the  dips 
being  between  40°  and  60°.  East  of  the  same,  separated  by  a  grassy  val- 
ley, is  another  lower  conglomerate  ridge,  with  a  few  verj^  steep  eastward 
dips,  and  a  greater  number  of  very  steep  westward  dips,  which  can  be  best 
summarized  as  steep,  nearly  vertical,  dips.  This  variation  of  dips  between 
the  two  ridges  admits  of  the  suggestion  that  there  is  a  syncline  between 
them.  Following  the  strike  of  the  nearly  verticall}^  dipping  ridge  north- 
ward, exposures  with  almost  vertical  dips  soon  cease.  Eastward-dipping 
exposures,  however,  continue  to  occur  northward,  suggesting  that  if  there  is 

1  Charles  D.  Walcott,  Biachiopod  fauna  of  the  quartzitic  pebbles  of  the  Carboniferous  conglom- 
erates of  the  Narragaiisett  Basin,  E.  I. :  Am.  Jour.  Sci.,  October,  1898,  3d.  series,  Vol.  VI,  p.  327. 


COARSE  CONGLOMERATE  OF  HANGING  ROCKS.  367 

a  closely  folded  synclinal  structure  with  its  axis  so  far  westward,  it  must  be 
of  limited  long-itudinal  extent. 

Hanging   Rock   ridge   possibly   the    eastern   side   of    an    anticlinal    fold. Tlie      HaUg'ing'      Rock 

coarse  conglomerate  ridge  also  ag-rees,  lithologically,  to  a  remarkable  degree 
with  the  Purgatory- Paradise  and  the  Sakonnet  River  western  shore  con- 
glomerate. Its  dips  are  verj?^  steep  to  the  westward.  If  the  two  western 
Paradise  ridges  were  considered  as  forming  a  close  syncline,  the  Hanging 
Rock  ridge  could  be  regarded  as  the  eastern  side  of  an  anticline  lying  east 
of  that  syncline.  The  various  exposures  of  conglomerate  east  of  the  Hang- 
ing Rock  ridge,  in  the  woods  and  in  the  fields  immediately  east  of  the 
stream,  would  then  necessarily  require  interpretation  as  the  eastern  side  of' 
a  second  syncline,  while  the  Sakonnet  River  western  shore  exposures  would 
in  their  turn  form  the  eastern  side  of  the  next  anticline.  In  the  absence  of 
clear  evidence  on  this  point,  the  steep,  nearly  vertical,  western  dip  of  the 
Hanging  Rock  ridge  is  almost  as  favorable  to  this  interpretation  as  to  any 
other,  although  requiring  an  anticlinal  fold  slightly  overturned  toward  the 
east  in  order  to  make  the  steeply  westward-dipping  Hanging  Rock  ridge 
the  eastern  side  of  an  anticlinal  fold. 

Dips  immediately  east  of  Hanging  Rock  ridge. OppOSitC    tllC      Uliddlc     leUgtll      of     tllC 

Hanging  Rock  ridge  a  small  conglomerate  ridge  forms  a  promontory  pro- 
jecting southward  into  Gardners  Pond.  Its  dip  is  from  80°  W.  to  vertical. 
On  the  southeastern  side  of  this  promontory  a  more  eastern  exposure  dips 
60°  E.  Northward  along  the  strike  from  this  promontory  the  dip  is  40°  E., 
and  remains  east  to  a  point  east  of  the  northern  end  of  the  Hanging  Rock 
ridge.  An  exposure  east  of  that  point  dips  80°  E.  These  dips  are  cer- 
tainly very  unfavorable  to  any  view  making  the  Hanging  Rock  ridge  the 
western  side  of  a  syncline  and  the  more  eastern  exposures  near  by ,  in  the 
woods  and  fields,  the  eastern  side,  as  suggested  in  the  preceding  paragraph. 
The  dips  at  the  Hanging  Rock  ridge  and  eastward,  if  considered  apart  from 
any  question  of  correlation  between  the  Hanging  Rock  conglomerate  and 
that  along  the  western  shore  of  the  Sakonnet  River,  are  certainly  more 
favorable  to  the  supposition  of  a  local  anticline,  and  this  is  the  view  taken 
by  Profs.  T.  N.  Dale,  Crosby,  and  Barton,  who  visited  this  locality  to 
compare  dissenting  opinions. 

Interpretation  adopted. — Thc  interpretation  adopted  by  the  writer  accepts  the 
eastward  dips  of  the  main  Purgatory-western  Paradise  ridge  as  indicative 


368  GEOLOGY  OF  THE  IS'^AEEAGAKSETT  BASIN. 

of  its  position  on  the  western  side  of  a  syncline.  It  ignores  the  fact  that 
a  smaller  ridge  immediately  toward  the  east  shows  much  steeper  and 
sometimes  somewhat  western  dips,  and  suggests  instead  that  these  more 
vertical  dips  arise  in  consequence  of  the  very  inflexible  character  of  this 
coarse  conglomerate,  even  under  conditions  of  strong  folding,  causing  the 
tilting  of  large  masses  at  unusual  angles.  The  thickness  of  conglomerate 
forming  the  lower,  more  eastern,  of  these  ridges  is  considered  entirely 
inadequate  for  correlation  with  the  much  greater  mass  of  conglomerate 
forming  the  larger,  more  western,  ridge,  which  is  so  great  as  not  to  admit  of 
the  interpretation  of  the  lower  ridge  as  forming  a  possible  repetition  of  the 
higher  one,  owing  to  the  intervening'  s}niclinal  structure  in  which  both  are 
involved. 

The  thickness  of  conglomerate  forming  the  Hanging  Rock  ridge  is 
considered  entirely  inadequate  for  correlation  with  the  much  greater  con- 
glomerate section  east  of  the  ridge  as  opposite  sides  of  the  same  anticline, 
the  Hanging  Rock  ridge  forming-  the  western  side,  and  the  field  exposures 
the  eastern  side.  Foi-  this  reason  the  Hanging  Rock  ridg-e  is  considered 
the  eastern  side  of  a  great  syncline,  with  the  Purgatory-Paradise  lidge  as 
the  western  side.  The  region  east  of  the  Hanging  Rock  ridge  is  considered 
as  anticlinal  in  structure,  with  the  Hanging  Rock  ridge  as  the  western  side 
of  the  anticline  and  the  Sakonnet  River  western  shore  conglomerate  as 
the  eastern  side.  This  interpretation  also  ignores  the  eastern  dips  of  the 
conglomerate  exposures  immediately  east  of  the  northei'n  half  of  the  Hang- 
ing Rock  ridge,  considering  these  ag-ain  as  mere  exadences  of  the  results 
possible  when  unusuallv  hard  rocks  are  subjected  to  processes  of  folding 
in  conjunction  with  great  masses  of  much  softer  underlying-  shales.  This 
interpretation  would  give  approximatelv  the  same  thickness  to  the  coarse 
conglomerates  involved  in  the  (1)  two  western  Paradise  ridges  west  of  the 
reservoir,  (2)  the  exposures  at  the  Hanging  Rock  ridge  and  those  imme- 
diately eastward,  and  (3)  the  western  shore  conglomerates  along  the 
Sakonnet  River. 

Southward  pitch  of  the  great  Paradise-Hanging  Rock  syncline. AcCCptlug  tlfis  interpreta- 
tion, the  Paradise  region  between  the  western  Paradise  ridge  and  the  Hang- 
ing Rock  ridge  is  to  be  considered  as  a  great  sjmcline.  The  conglomerate 
exposed  along  the  roadside  about  a  mile  southwest  of  Black  Point  is  con- 
sidered the  most  northern  exposure  of  this  syncline.     Its  elevation  is  about 


WESTEEN  COAiiSE  CONGLOMEEATE  EXPOSUEES,  369 

75  feet.  If  it  lies  anywhere  near  tlie  base  of  the  syncline  the  trough  dips 
strongly  southward,  since  the  base  of  the  conglomerate  series  near  the 
southern  end  of  the  Paradise  region  must  lie  far  below  sea  level.  The 
qiiartzitic  shales  forming  the  central  parts  of  the  Paradise-Hanging  Rock 
area  southward  are  considered  as  pre-Carboniferous,  the  intercalated 
igneous  rocks  having  penetrated  these  shales,  but  not  the  rocks  of  Carbon- 
iferous age. 

Southward  pitch  of  the  Sakonnet  River  syncline. The   SyncliuC  bctweeU  SmltllS  Bcach, 

Taggarts  Ferry,  and  Black  Point  on  the  west,  High  Hill  Point  on  the 
north.  Windmill  Hill  on  the  northeast,  and  an  unexposed  region  now  occu- 
pied by  the  eastern  part  of  the  lower  Sakonnet  River  has  already  been 
mentioned.  The  shore  exposures  west  of  Windmill  Hill  as  far  as  Browns 
Point  must  once  have  underlain  a  continuation  of  the  coarse  conglomerate 
series  still  exposed  at  High  Hill  Point  and  on  the  side  of  Windmill  Hill,  if 
such  a  synclinal  structure  really  exists.  At  High  Hill  Point  the  conglom- 
erate is  exposed  at  sea  level.  Southward,  opposite  Taggarts  Ferry  and 
Smiths  Beach,  the  base  of  the  syncline  must  lie  far  below  sea  level,  indi- 
cating a  southward  pitch  of  the  syncline  and  adding  another  instance  of 
the  general  southward  pitching  of  the  rocks  in  southern  Aquidneck. 

From  High  Hill  Point  to  the  northwestern  side  of  Nonquit  Pond,  and 
thence  to  the  eastern  side  of  Nannaquacket  Pond,  the  coarse  conglomerate 
is  exposed  at  about  sea  level  and  rises  to  about  80  feet  above.  The  Fog- 
land  Point  conglomerate  is  also  at  about  sea  level.  The  syncline  probably 
does  not  extend  far  north  of  High  Hill  Point. 

WESTERN   COARSE  CONGLOMERATE  EXPOSURES. 

Lithologically  the  coarse  conglomerates  of  Miantonomy  Hill  and 
Coasters  Harbor  Island  present  all  the  features  of  the  Purgatory  coi.l- 
glomerates  on  the  east,  excepting  the  marked  elongation  of  the  pebbles. 
Since  the  elongation  of  the  pebbles,  wherever  it  occurs,  is  a  secondary 
feature,  it  need  not  be  taken  into  account. 

Possible  syncline  immediately  west  of  Miantonomy  Hill. At  MiaUtOUOmy  Hill  thc  COarSC 

conglomerate  pitches  southward  at  an  angle  of  perhaps  15°,  conglomerate 
occurring  again  at  a  lower  level  an  eighth  of  a  mile  south  of  the  summit 
of  that  hill.  On  Beacon  Hill,  immediately  northward,  a  conglomerate  is 
exposed,  with  pebbles  usually  not  exceeding  8  inches  in  length.  The  over- 
MON  xxxiii 24 


370  GEOLOGY  OF  THE  NARRAGANSETT  BASIN. 

lying  sandstone  indicates  also  a  southward  pitch,  and  a  westward  dip  on 
the  western  side  of  Beacon  Hill.  In  a  field  west  of  Miantonomy  Hill,  near 
the  railroad,  coarse  conglomerate  dips  45°  E.,  suggesting  a  S3^nclinal 
structure  between  the  conglomerate  exposed  in  the  field  and  that  on  the 
hill.  This  interpretation  would  demand  an  anticlinal  structure  west  of  the 
first-named  exposure,  a  synclinal  structure  coming  in  again  at  Coddington 
Point  and  Coasters  Harbor  Island,  where  coarse  conglomerate  again 
appears,  that  of  Coasters  Harbor  Island  bearing  the  closest  resemblance  to 
that  on  Miantonomy  Hill. 

This  interpretation  of  the  geological  structure  is  again  very  free,  and 
is  based  upon  two  assumptions :  That  the  conglomerate  exposures  on 
Miantonomy  Hill  and  those  at  Coasters  Harbor  Island,  lithologically  alike, 
are  also  stratigraphically  identical,  and  that  the  field  exposures  of  con- 
glomerate which  dip  eastward  possibly  belong  to  the  same  horizon. 

Possibility  of  two  horizons  of  conglomerate  at  Miantonomy  Hill.  Why,      hoWCVCr,      should 

there  not  be  two  horizons  of  conglomerate,  the  exposures  west  of  Mianto- 
nomy Hill  underlying  the  coarse  conglomerate  forming  the  summit  of  that 
hiir?  The  occurrence  of  coarse  conglomerate  low  down  in  the  Aquidneck 
series — in  fact,  according  to  our  interpretation,  at  its  base,  in  the  western 
part  of  Bristol  Neck — shows  the  possibility  of  coarse  conglomerate  lower 
than  that  which  forms  the  summit  of  the  rock  of  Carboniferous  age  in  the 
Narragansett  Basin.  Possibly  this  exposure  west  of  the  hill  is  such  a  lower 
horizon,  although  not  near  the  base  of  the  shale  series. 

On  the  western  side  of  the  stream  entering  Eastons  Pond  from  the 
north,  in  the  fields  north  of  the  first  east-west  road,  is  a  conglomerate 
exposure  apparently  dipping  very  low  to  the  westward,  so  that  the  dip 
would  evidently  carry  also  this  conglomerate  beneath  the  conglomerate 
forming  the  summit  of  Miantonomy  Hill.  The  exposure  of  conglomerate 
north  of  Eastons  Pond  might  therefore  correspond  to  the  section  west  of 
Miantonomy  Hill,  the  two  forming  a  lower  horizon  of  conglomerate,  while 
the  Miantonomy  Hill  exposure  formed  the  upper  horizon.  To  wliich  of 
these  two  horizons  would  the  Coasters  Harbor  Island  conglomerate 
belong?  The  writer  interprets  it  as  corresponding  to  the  Purgatory 
conglomerate.  Its  resemblance  to  the  conglomerate  near  the  summit  of 
Miantonomy  Hill  is  so  great  as  to  be  considered  conclusive  of  identity, 
notwithstanding  the  fact  that  conglomerates  corresponding  to  these  expo- 


GEOLOGICAL  POSITION  OF  NEWPORT  (JLIFF  CONGLOMEKATES.      37  i 

sures  do  not  occur  at  intermediate  localities.  The  absence  of  these  con- 
glomerates at  Coddington  Point  is  also  puzzling. 

Interpretation  adopted. — So  moderate  a  thickucss  of  coarse  conglomerate  is 
exposed  in  the  fields  northwest  of  Eastons  Pond  and  west  of  Miantonomy 
that  it  is  impossible  confidently  to  identify  them  with  the  much  thicker 
Purgatory  conglomerate.  The  Miantonomy  Hill  and  Coasters  Harbor 
Island  exposures,  on  the  contrary,  suggest  a  much  thicker  section  than 
the  field  localities,  and  show  pebbles  of  a  size  more  nearl}^  corresponding 
with  that  of  the  coarse  Purgatory  conglomerate.  For  this  reason  the  writer 
considers  the  Miantonomy  Hill  exjiosure  equivalent  to  the  Pin-gatory  con- 
glomerate, the  Coasters  Harbor  Island  conglomerate  being  referred  to  the 
same  horizon.  Whether  the  field  exposures  are  to  be  considered  as  belonging 
to  the  same  general  horizon  or  not  is  left,  for  the  present,  an  open  question. 

Geological    position   of   the    Newport    Cliff    section. Tho      gCological       pOSitioU      of      the 

Newport  Cliff"  exposm-es  presents  another  important  question,  to  which  an 
uncertain  answer  must  be  returned.  The  conglomerate  on  Miantonomy 
Hill  pitches  southward  about  15°.  If  it  has  any  representative  southward 
which  is  actually  exposed,  it  is  almost  certainly  the  upper  part  of  the  New- 
port Cliff"  section,  toward  Ochre  Point.  Here  conglomerate  occurs  in  layers 
which  are  interbedded  with  a  greater  percentage  of  sandstone  and  shale 
than  is  found  in  the  Purgatory-Paradise  or  in  the  Black  Point-Smiths 
Beach  coarse  conglomerate  sections.  The  pebbles,  moreover,  are  commonly 
not  so  large,  although  several  layers  with  fairly  large  pebbles  occur,  and 
locally  some  very  large  pebbles  are  found,  a  few  exceeding  15  inches  in 
diameter.  Some  of  the  largest  pebbles  may  be  seen  west  of  Oclire  Point 
in  a  very  thin  conglomerate  layer,  at  the  top  of  the  conglomerate  series. 
The  sandstones  and  shales  interbedded  with  these  coarser  conglomerates  are 
more  frequently  greenish  and  brownish  than  similar  rocks  farther  down  in 
the  cliff  section. 

If  the  upper  and  coarser  conglomerate  beds  of  the  New^^ort  Clitf  sec- 
tion be  considered  the  equivalent  stratigraphically  of  the  Miantonomy 
Hill  section,  the  lower  part  of  the  Newport  Cliff"  section  at  once  demands 
attention  on  account  of  its  peculiar  lithological  characteristics.  This  part 
of  the  section  also  contains  frequent  conglomei-ate  lavers,  although  the 
pebbles  are  rather  small  or  of  only  medium  size.  The  interbedded  sand- 
stones are  often  darkened  by  the  presence  of  carbonaceous  matter,  and  the 


372  GEOLOGY  OF  THE  FAEEAGANSETT  BASIlSf. 

shales  are  frequently  carbonaceous  or  coaly.  Exposures  beneath  the 
Miantonomy  Hill  conglomerate  are  few  and  do  not  resemble  very  closely 
the  lower  part  of  the  Newport  Cliff  section.  There  is  no  probability  of 
a  considerable  amount  of  mediiim-pebbled  conglomerate  underlying  the 
coarser  bed  at  Miantonomy  Hill,  so  that  the  Newport  Cliff  section  appears 
very  much  richer  in  conglomerate  layers  in  that  part  of  the  section  which 
immediately  underlies  the  coarser  conglomerates. 

If  the  coarse  conglomerates  of  the  Newport  Cliff  section  be  compared 
with  the  Purgatory  conglomerate,  then  the  underlying  medium-pebbled 
conglomerates  toward  the  "Forty  Steps"  and  the  western  end  of  Eastons 
Beach  must  correspond  to  the  medium-pebbled  conglomerate  laj^ers  of 
much  smaller  thickness  beneath  the  Purgatory  conglomerate  at  Eastons 
Point.  In  other  words,  the  Sakonnet  sandstones  of  Black  Point,  along  the 
Sakonnet  River,  wou.ld  be  represented  at  (1)  Eastons  Point  by  a  few  con- 
glomerate layers  with  medium-sized  pebbles  scattered  rather  irregularly 
among  the  much  more  abundant  shales  and  sandstones,  and  at  (2)  the  Newport 
Cliffs  by  a  greater  quantity  of  conglomerate  in  a  section  of  greater  thickness. 

The  real  difficulty  in  the  way  of  a  satisfactory  interpretation  of  the 
geological  position  of  the  Newport  Cliff  exposures  is  the  paucity  of  outcrops 
between  these  cliffs  and  Miantonomy  Hill,  or  between  the  cliffs  and  Eastons 
Point.  Too  little  is  also  known  of  the  rocks  underlying  Newport.  It  may 
be  that  others,  who  resided  in  Newport  at  the  time  the  various  sewers  were 
constructed,  have  the  necessary  information,  but  all  that  the  writer  could 
leam  was  insufficient  to  determine  the  correlation  of  the  beds.  The 
writer's  experience  is  that  isolated  exposures  of  small  area  are  very  unsafe 
for  the  determination  of  horizons  where  the  lithological  character  of  the 
rocks  change  so  often  as  they  do,  for  instance,  at  the  Newport  Cliffs.  Con- 
tinuous sections  are  needed.  Until  further  evidence  is  secured  the  writer 
prefers  to  consider  the  Newport  Cliff  section  the  equivalent  of  the  Mian-- 
tonomy  Hill  and  the  Eastons  Point  sections  in  the  sense  described  above. 

Prof.  T.  Nelson  Dale  mentions  that  coal  seams  were  struck  in  digging- 
wells  under  the  city  of  Newport.  Coal  seams  formerly  outcropped  near 
Sheep  Point,  on  the  cliffs.  Coal  plants  have  been  found  near  the  corner  of 
Marlborough  and  Farewell  streets.^    In  his  published  sections  he  places  coaly 

•  In  a  sewer  tunnel  made  nearly  ten  years  ago,  between  Bellevue  avenue  and  the  first  avenue 
parallel  to  it  on  the  east,  and  not  far  north  of  Ochre  Point,  Carbonaceous  shale  formed  the  rock 
exposure.     It  was  examined  by  Professor  Dale. 


COARSE  CONGLOMERATE  OF  NORTHERN  AQUIDNECK.         3Y8 

shales  beneath  the  city  of  Newport.  The  contact  with  the  top  of  the  coarse 
conglomerate  is  unconformable.  Coaly  shales  of  considerable  extent  are, 
however,  suggestive  of  Aquidneck  shales,  since  these  are  the  only  shales 
having  any  great  distribution  over  wide  areas.  This  would  place  the  rocks 
beneath  the  city  of  Newport  in  the  Aquidneck  series  and  beneath  the  cliff 
exposure.  Either  a  fault  or  a  close  overturned  synclinal  fold  must  be 
hypothesized  to  account  for  the  present  position  of  these  rocks.^  Professor 
Dale  notes  the  presence  of  slates  and  conglomerates  at  Emmanuel  Chapel,  at 
the  corner  of  Spring  and  Perry  streets.    Conglomerates  occur  in  Morton  Park. 

Portsmouth  synclinal  conglomerate. Near    the     SUmmlt     of    tllO     PortSmOUtll    S}T1- 

cline  the  upper  green  shales  begin  to  contain  sandstone  and  some  small- 
pebbled  conglomerate  layers,  overlain  at  various  localities,  it  seems,  by 
sandstone  and  coarse  conglomerate.  Coarse  conglomerate  occurs,  for 
instance  a  third  of  a  mile  south  of  Butts  Hill,  in  the  Portsmouth  camp- 
meeting  grounds  north  of  Qtiaker  Hill,  and  on  the  east  side  of  the  Newport- 
Bristol  Ferry  road,  half  a  mile  west  of  Quaker  Hill.  This  conglomerate, 
associated  with  much  sandstone,  is  believed  to  have  been  introductorv  to 
the  coarse  conglomerate  series,  which  once  must  have  lain  above  it. 

East  of  the  Portsmouth  syncline  there  must  have  been  an  anticline 
(merging  southward  perhaps  into  a  monocline),  in  order  to  enable  the 
coarse  conglomerate  to  appear  at  sea  level  on  the  eastern  side  of  the  Sakon- 
net  River  from  Fogland  Point  to  the  eastern  side  of  Nannaquacket  Pond. 

Conglomerates  of  Warren  Neck  and  Swansea. Tho     COarSO     COUglomCrate     eXpOSUreS 

from  the  western  side  of  Warren  Neck  to  Coles  Station,  along  both  banks 
of  Lees  River  north  of  the  southern  road  to  Fall  River,  and  thence  north- 
ward to  Swansea  village,  as  well  as  the  exposures  found  north  of  the  west- 
ern Warren  Neck  exposures,  at  Luthers  Corner  and  in  western  Swansea, 
are  all  considered  as  corresponding  to  the  coarse  conglomerate  series  lying 
to  the  southward. 

Thickness  of  the  coarse  conglomerate. — The  tluckuess  of  the  coarse  couglomcrato 
in  the  Black  Point-Taggarts  Ferry  section  was  estimated  to  be  at  least  380 
feet.     This  may  not  include  the  entire  section,  a  part  of  the  conglomerate 

1  Prof.  T.  Nelson  Dale,  in  his  paper  ou  the  Geology  of  the  Month  of  Narragansett  Bay  (Proo. 
Newport  Nat.  Hist.  Soc,  Document  3,  pp.  6-14,  Newport,  E.  I.,  1885),  gives  a  somewhat  different 
interpretation  of  the  general  section  of  this  part  of  the  basin  from  that  presented  by  Dr.  Foerste. 
The  most  notable  dift'erence  concerns  the  position  of  the  quartzite  conglomerate,  which  Dale  places 
below  the  coal-bearing  portion  of  the  section. — N.  S.  S. 


874  GEOLOGY  OF  THE  NAERAGANSETT  BASIN. 

being  possibly  not  exposed.  Tlie  Purgatory-Paradise  section  of  coarse  con- 
glomerate may  range  between  600  and  450  feet  in  thickness,  according  as  the 
lower  and  eastern  one  of  the  two  ridges  is  or  is  not  included  in  the  section. 
Fossil  localities. — Fcms  are  found  in  Woods  Castle,  in  a  coaly  shale  which 
belongs  stratigraphically  within  the  coarse  conglomerate  series.  They 
occur  also  in  the  Newport  Cliffs  a  short  distance  south  of  Marys  Seat,  in  a 
coaly  black  shale  about  14  feet  thick,  overlying  a  conglomerate  bed  about 
11  feet  thick,  with  pebbles  often  4  inches  thick.  Fossil  ferns  are  still  more 
common  in  the  coaly  shales  southwest  of  Oclu"e  Point,  near  the  top  of  the 
sea  wall.  The  position  of  these  coaly  shales  is  not  accurately  known. 
They  lie  west  of  the  Newport  Cliff  section  with  its  conglomerates,  but  may 
belong  to  the  shale  series  exposed  beneath  Newport.  This,  according  to 
the  writer's  interpretation,  would  place  them  below  the  coarse  conglomerate. 


CHAPTER    X. 

THE  ARKOSES  AND  BASAL  CONGLOMERATES. 

]S"ATICK  ARKOSE. 

From  Natick  to  Cranston. — Aloiig  the  steop  luU  facG  from  Natick,  Rliocle  Island, 
for  2^  miles  northward  into  Cranston,  extend  the  arkoses  and  qnartzite  con- 
glomerates that  form  the  lowest  rocks  of  Carboniferous  age  on  the  western 
side  of  Narragansett  Basin.  The  eastward  dip  of  these  rocks  shows  their 
position  beneath  the  Kingstown  series,  which  lie  farther  eastward.  Near 
the  fork  of  the  road,  half  a  mile  northwest  of  Natick,  a  coaly  black  shale 
overlies  the  arkose  and  is  itself  overlain  by  a  qtiartzitic  sandstone  contain- 
ing large  quartzite  pebbles.  The  arkose  consists  largely  of  detrital  quartz 
derived  from  decayed  granite,  and  is  usually  found  near  those  localities 
where  the  immediately  underlying  pre-Cai'boniferous  rocks  consist  chiefly 
of  granite.  The  quartzite  conglomerate  is  usually  found  near  pre-Carbon- 
iferous  quartzite  beds,  and  near  contact  with  the  latter  the  round  pebbles 
give  way  in  places  to  those  of  such  angular  contours  as  to  warrant  giving 
the  name  of  breccias  to  the  lowest  layers.  This  is  es2Decially  true  of  the 
exposiu-es  at  Alexander  McTeer's  house,  north  of  Natick.  Granite  pebbles 
are  rare,  owing  to  lack  of  firmness  on  the  part  of  the  g'ranite  in  the  original 
ledges  at  the  time  the  arkose  was  formed.  Of  course  the  arkose  forms  a 
part  of  the  detrital  material  between  the  pebbles  of  the  coarse  conglom- 
erates, and  quartzite  pebbles  are  not  rare  in  some  of  the  beds  of  arkose. 
In  some  cases  the  basal  arkoses  and  quartzitic  conglomerates  do  not  exceed 
100  feet  in  thickness,  and  a  thickness  of  200  feet  seems  not  to  be  attained 
in  any  single  set  of  exposures.  Some  of  the  pebbles  in  these  basal  con- 
glomerates are  15  inches  in  length. 

Northward,  in  the  southern  part  of  the  field  studied  by  Mr.  Wood- 
worth,  the  basal  arkoses  and  C(5nglomerates  do  not  long  continue  to  be 
exposed,  although  the  steep  escarpment  still  outlines  approximately  the 
position  of  these  basal  deposits. 

The  basal  arkose  and  conglomerate  beds  along  the  western  border  of 
the  Carboniferous  basin  are  believed  to  represent  the  oldest  Carboniferous 
rocks  in  the  areas  bordering  Narragansett  Bay.     They  are  not  a  formation 


376  GEOLOGY  OF  THE  NAREAGANSETT  BASIK 

distinct  from  the  Kingstown  series,  but  represent  the  lowest  beds  of  the 
Kingstown  sandstones  and  shales.  The  detrital  material  of  which  they 
ai'e  composed  is  evidence  of  the  fact  that  areas  of  granite  lay  sufficiently 
near  to  provide  the  quartz  and  cementing  material  of  the  arkose.  The 
angular  breccia  conglomerate  at  places  north  of  Natick  suggests  that  both 
granite  and  quartzite  existed  at  no  great  distance  from  the  present  location 
of  these  beds.  If  this  surmise  be  correct,  we  have  a  right  to  assume  the 
existence  of  land  areas  somewhere  in  this  region.  This  does  not  demand 
that  the  present  granite  and  quartzite  escarpment  should  have  been  a  shore 
line  at  the  time  the  Carboniferous  deposits  of  the  Narragansett  Basin  were 
formed.  It  is  not  probable  that  the  land  areas  of  that  time  were  bordered 
by  such  straight  and  abrupt  escarpments. 

The  present  granite  and  quartzite  escarpments  had  probably  the  fol- 
lowing history:  Before  the  deposition  of  the  Carboniferous  deposits  a 
widely  extended  area  of  granite,  quartzites,  and  pre-Carboniferous  shales 
formed  the  iioor  of  the  basin.  Part  of  this  floor  was  above  water  level, 
and  furnished  materials  for  arkose  and  conglomerates.  The  lowering  of 
the  basin  and  the  progressive  overlapping  of  later  deposits  may  have 
entirely  covered  up  these  land  areas  and  cai'ried  the  shore  line  much  farther 
westward.  The  direction  and  location  of  these  early  shore  lines  are  in 
reality  not  known.  Subsequent  to  the  deposition  of  the  Carboniferous 
the  rocks  of  the  entire  basin  were  subjected  to  strong  folding,  the  axes  of 
the  folds  running  north-south.  The  granite  and  quartzite  escarpment  on  the 
western  side  of  the  bay  represents  the  bed  of  the  Carboniferous  deposits, 
brought  up  on  the  western  side  of  a  great  synclinal  fold.  The  escarpment 
is  due  to  subsequent  erosion. 

Base  of  the  Carboniferous  south  of  Natick. A     mile     SOUtll    of    DavisviUe,    aloUg    the 

railroad,  an  abundant  supply  of  conglomerate  is  to  be  referred  rather  to 
the  base  of  the  Kingstown  series  than  to  the  basal  beds  above  mentioned. 
From  Natick  to  East  Greenwich  and  Wickford  Junction  the  steep  escarp- 
ment continues  to  indicate  approximately  the  horizon  along  which  the  basal 
deposits  occur,  but  no  exposures  are  found. 

South  of  Wickford  Junction  it  is  impossible  to  identify  the  basal 
deposits  of  the  Carboniferous  series.     It  is  possible  that  they  are  not  exposed. 

Probable  relations   between    the   various   granites   and   pegmatites   and  the  Carboniferous  beds. 1  [iQ 

writer   is  inclined    to  favor  the   view  that  the  Carboniferous  series  once 


ARKOSE  OF  WESTERN  BORDER  OF  BASIN.  377 

extended  from  the  shore  exposures  near  Saunderstown  and  the  Bonnet  over 
unbroken  areas  as  far  west  at  least  as  McSparran  and  Tower  hills,  and 
covered  even  Boston  and  Little  necks  as  far  south  as  Nan-agansett  Pier. 
The  basal  Carboniferous  of  these  regions  probably  rested  upon  an  extensive 
pre-Carboniferous  granite  area.  In  consequence  of  folding,  the  pre-Carbon- 
iferous  granite  was  raised  toward  the  west  of  the  Tower  and  McSparran 
escarpments  and  along  the  area  now  occupied  by  Little  and  Boston  necks, 
while  the  Carboniferous  was  lowered  into  a  synclinal  tract  lying  between 
these  two  regions  along  the  Cove  and  the  Pattaquamscott,  and  was  by 
later  denudation  severed  from  the  Carboniferous  east  of  Boston  Neck. 

There  is  undoubted  evidence  of  faulting  in  the  Carboniferous  area 
east  of  Boston  Neck.  The  temptation  is  ver}^  great  to  account  for  the 
alternation  of  granite  and  Carboniferous  rock,  in  part  at  least,  by  faulting. 
Some  of  the  occurrences  of  detrital,  presumably  Carboniferous,  masses  m 
the  granite  areas,  however — for  instance,  those  at  Narragansett  Pier  and  at 
Clump  Rocks  light-house — could  be  explained  as  cases  of  Carboniferous 
rocks  once  overlying  the  granites,  but  subsequently  broken  up  and  folded 
in  with  the  granites,  or  faulted  down  into  them  by  later  disturbances,  only 
remnants  of  the  Carboniferous  rocks  remaining,  owing  to  denudation.  Or 
else  they  must  be  considered  as  fragments  of  Carboniferous  rocks  caught 
up  by  post-Carboniferous  granites.  Unfortunately,  post-Carboniferous 
granites  are  not  known  anywhere  in  the  field  here  investigated. 

Where  the  Carboniferous  rocks  are  traversed  by  dike-like  rocks,  the 
latter  on  closer  examination  almost  invariably  tiu-n  out  to  be  pegmatitic  in 
structure,  so  that  the  pegmatites  are,  as  a  rule,  readily  identified  as  post- 
Carboniferous.  These  coarse  pegmatites  traverse  the  Carboniferous  rocks 
rather  frequently  south  of  Hazzard's  quarry  and  Saunderstown  as  far  as  the 
region  northwest  of  the  cove,  and  are  especially  well  exposed  at  Watsons 
Pier  (PL  XXV;  see  also  Pis.  XVIII  and  XIX,  pp.  242,  244).  But  the 
mass  of  pegmatite  southwest  of  Wesqxiage  Pond,  on  the  hill,  seems  to 
belong  to  the  Boston  Neck  series  of  exposures,  and  appears  to  connect 
with  pre-Carboniferous  granites  as  though  the  latter  were  in  reality  post- 
Carboniferous.  The  conditions  are  perplexing  and  require  more  study.  It 
may  be  that  careful  observations  might  lead  to  more  definite  results,  but 
to  the  writer  conclusive  data  seem  to  be  lacking,  although  he  considers  the 
general  mass  of  g-ranites  as  pre-Carboniferous. 


378  GEOLOGY  OF  TPIE  NAREAGANSETT  BASIK 

The  question  suggests  itself  whether  Indian  Run  represents  another 
synchne  within  the  granite  area  which  contains  Carboniferous  rocks.  This 
area  has  not  been  carefully  investigated.  The  writer  is  inclined  to  consider 
McSparran  and  Tower  hills  as  marking  the  most  western  exposures  of 
Carboniferous  rocks  in  the  basin,  without  any  attempt  to  assert,  however, 
that  in  times  preceding  the  folding  and  subsequent  denudation  the  Car- 
boniferous rocks  could  not  have  extended  farther  westward.  If  it  be 
remembered  that  the  Carboniferous  deposits  half  a  mile  south  of  Bridge- 
town and  along  southern  Tower  Hill  owe  their  high  inclination  to  folding, 
it  will  be  seen  from  a  restoration  of  these  beds  to  their  original  horizontal 
attitudes  that  Carboniferous  beds  must  have  once  extended  farther  west- 
ward, making  the  western  shore  line  pass  west  of  Tower  Hill;  how  much 
farther  west  is  not  known. 

TIVEKTOX  ARKOSE. 

From  Steep  Brook  to  Nannaquacket  Pond. — Aloug  the  pre-Carbouiferous  escarpmcut 
extending  from  Steep  Brook  to  Tiverton  Four  Corners  a  number  of  expo- 
sures of  arkose  occur.  Since  this  escarpment  consists  almost  entirely  of 
granite,  any  overlying  basal  Carboniferous  rocks  are  apt  to  include  arkose 
beds.  The  latter  were  formerly  well  exposed  at  Steep  Brook,  but  this  is  no 
longer  the  case.  A  fine  exposure  occurs  in  Fall  River,  another  at  Town- 
send  Hill  in  the  northwestern  end  of  the  town  of  Tiverton,  one  at  the 
quarry  northeast  of  Tiverton  railroad  bridge,  and  there  are  several  expo- 
sures along  the  escarpment  east  of  Nannaquacket  Pond  in  Tiverton.  In 
all  of  these  localities  carbonaceous  shales  are  more  or  less  intimately  asso- 
ciated with  the  arkoses.  At  Steep  Brook  and  Fall  River  these  were  fern 
bearing.  East  of  Nannaquacket  Pond  and  at  Fall  River  the  arkoses  and 
coaly  shales  alternate  repeatedly.  At  Steep  Brook  and  the  quarry  northeast 
of  the  Tiverton  railroad  bridge  conglomerate  beds  occur  in  close  connection 
with  the  arkose  series.  The  fact  that  these  conglomerates  contain  quartzite 
pebbles  similar  to  those  in  the  Natick  conglomerates  and  that  the  pebbles 
in  places  attain  a  length  of  6  inches  does  not  simplify  the  problem,  since 
pre-Carboniferous  quartzites  are  practically  unknown  on  the  eastern  side  of 
the  basin.  The  pre-Carboniferous  quartzites  on  the  eastern  side  of  the 
basin  may  have  been  removed  by  subsequent  erosion,  but  there  is  no  good 
reason  for  assuming  their  former  existence  here.  The  thickness  of  the 
Tiverton  arkose  series  is  usually  less  than  100  feet  and  is  nowhere  known 
to  exceed  200  feet. 


SAOHUEST  ARKOSE.  379 

South  of  Nannaquacket  Pond. — Tlie  stecp  escarpmeiit  soutlieast  of  Nannaquacket 
Pond  locates  approximately  the  line  along  which  the  arkose  beds  may 
occur  farther  soiithward. 

Equivalence   of  the    Tiverton   arkoses  to  [those  near   Natick. The      COarSC      COnglomerateS 

assigned  to  the  top  of  the  Carboniferous  series  on  the  eastern  side  of  the 
basin  overlie  these  arkoses  within  such  a  limited  distance  that  it  seems 
hardly  credible  to  sujopose  that  if  the  coarse  conglomerates  along  the 
Sakonnet  River  correspond  to  the  Purgatory  conglomerates  the  arkoses  on 
the  eastern  side  of  the  basin  may  correspond  to  the  Natick  arkoses  and 
conglomerates.  Yet  something  of  this  relationship  must  be  assumed,  with 
the  jiossibility,  however,  of  considering  the  Tiverton  arkoses  perhaps  not 
so  old  as  those  occurring  on  the  western  side  of  the  bay,  their  basal  posi- 
tion not  certifying  to  absolute  equality  of  age  with  the  Natick  exposures, 
but  only  to  their  early  deposition  as  compared  with  other  deposits  on  the 
eastern  side  of  the  Carboniferous  field.  For  the  present,  faulting  is  assumed 
to  account,  in  part,  for  the  remarkably  short  distance  intervening'  between 
the  coarse  so-called  Purgatory  conglomerate  in  these  regions  and  the  basal 
Tiverton  arkoses,  but  the  absence  of  the  Kingstown  series  would  also  partly 
explain  the  facts.  The  escarpment  from  Steep  Brook  to  Tiverton  and 
thence  east  of  Nannaquacket  Pond  indicates  that  the  eastern  floor  of  the 
basin,  upon  which  the  Carboniferous  rocks  were  deposited,  consisted  largely 
of  granitic  rocks.  Subsequent  folding  Las  placed  them  upon  the  eastern 
side  of  a  great  synclinal  fold,  and  subsequent  denudation  has  left  behind  the 
present  escarpment.  The  original  contours  of  the  Carboniferous  basin  are 
unknown. 

SACHUBST  ARKOSE. 

The  western  and  southern  shores  of  Sachuest  Neck,  the  northern  shore 
at  Flint  Point,  and  a  small  exposure  ofiPshore  at  a  headland  a  quarter  of  a 
mile  south  of  Flint  Point  consist  of  arkose  with  which  more  or  less  coaly 
shale  is  interbedded.  Lithologically  it  strongly  resembles  the  exposures 
east  of  Nannaquacket  Pond,  and  it  contains  ferns  in  the  shale  beds,  as  was 
also  the  case  at  Fall  River  and  Steep  Brook.  If  the  writer's  view  as  to  the 
geology  of  this  region  is  correct,  the  arkose  of  Sachuest  Neck  rests  upon 
Cambrian  conglomerate  and  shale,  and  derived  its  materials  from  jjre- 
Carboniferous  granite.  The  total  thickness  of  these  arkose  beds  may 
amount  to  20i)  feet. 


380  GEOLOGY  OF  THE  NAREAGANSETT  BASIN. 

CONAlSriCUT    ARKOSE. 

On  the  eastern  side  of  Mackerel  Cove  arkose  is  found  exposed  north 
of  the  granite  area.  It  is  evidently  composed  of  the  detrital  material 
derived  from  the  granite,  and  the  latter  is  considered  pre-Carboniferous. 

The  statement  that  the  arkose  underlies  the  green  shale  is  an  assump- 
tion. The  thin  arkose  layers  in  the  black  shale  at  Beaver  Head  should  be 
noted  in  this  connection,  since  they  evidently  occur  at  the  base  of  the 
Aquidneck  shale  series.  Possibly  the  Mackerel  Cove  arkose  is  also  con- 
temporaneous with  part  of  the  Aquidneck  shales. 

ROSE    ISLAND    AND    COASTERS    HARBOR    ISLAND    ARKOSE. 

Arkose  and  black  shale  occur  on  Rose  Island  and  at  the  southern  end 
of  Coasters  Harbor  Island.  The  writer  has  felt  strongly  inclined  to  consider 
the  arkose  exposed  on  Conaniciit  and  on  the  islands  last  mentioned  as 
deposits  formed  in  the  proximity  of  a  great  pre-Carboniferous- granite  area, 
without  any  attempt  to  closely  synchronize  the  various  exposures.  Thus, 
the  arkose  at  the  southern  end  of  Coasters  Harbor  Island  may  belong,  as 
far  as  relative  age  is  concerned,  higher  in  the  Carboniferous  series  than 
the  arkose-  on  Conanicut  Island.  The  fact  that  it  appears  so  close  to  the 
coarse  conglomerate  on  Coasters  Harbor  Island  suggests  tlois.  But  this  is 
another  point  which  must  be  left  doubtful. 

If  the  green  and  purple  shales  of  the  Newport  Harbor  Islands,  of  New- 
port Neck,  and  of  Sachuest  Neck  are  of  Cambrian  age,  as  suggested,  these 
shales,  together  with  the  granite,  probably  formed  exposed  land  areas  in 
the  near  vicinity  in  early  Carboniferous  times.  The  progressive  overlap- 
ping of  Carboniferous  deposits  caused  arkose  beds  to  be  formed,  resting 
upon  the  lowered  Cambrian  formations.  This  would  account  for  the  close 
geographical  association  between  arkose  and  green  shale  or  other  pre- 
Carboniferous  rocks  in  these  areas.     Faulting  has  obscured  this  relation.-' 

Arkose  is  also  found  west  of  Ochre  Point,  east  of  Newport.  Perhaps 
in  all  of  the  cases  here  cited,  from  Conanicut,  Rose  Island,  Coasters  Harbor 
Island,  and  west  of  Ochre  Point,  the  arkose  is  to  be  considered  as  contem- 
poraneous with  some  part  of  the  Aquidneck  shale  series. 

The  arkose  on  Conanicut  maj  reach  a  thickness  of  100  feet.  The 
deposits  on  Rose  Island  and  Coasters  Harbor  Island  are  much  less  thick. 


'  T  N.  Dale,  Am.  Jour.  Sci.,  3d  series,  Vol.  XXVII,  pp.  217-228,  282-289,  map,  1884. 


CHAPTER    XI. 

THE  PRE-CARBONIFEROUS  ROCKS. 

The  pre-Carboniferous  rocks  of  the  basiu  usuall}'  consist  of  granite, 
often  rendered  gneissoid  by  shearing.  In  a  number  of  locahties  undoubted 
clastic  rocks  appear.  This  is  true,  for  instance,  of  the  western  tliird  of 
Newport  Neck,  from  Brentons  Point  to  Brentons  Cove,  of  all  of  the  New- 
port Harbor  Islands,  and  of  some  of  the  shore  exposures  along  the  southern 
margin  of  the  harbor.  The  shales  here  are  often  purplish  and  sometimes 
contain  thin  layers  of  limestone.  At  various  points  along  the  southern 
Newport  Harbor  region  rather  thick  layers  of  limestone  occur,  in  striking 
contrast  to  the  absence  of  limestones  in  the  Carboniferous  series.^  The 
purplish  or  greenish  shales  are  frequently  interbedded  with  a  more  quartz- 
itic  greenish  or  whitish  rock,  sometimes  shaly,  but  usually  more  like  argillite. 

Similar  rocks  are  found  along  the  eastern  shore  of  Sakonnet  River 
from  Browns  Point  to  the  granite  area  a  mile  north  of  Sakonnet  Breakwater. 
The  same  purplish-colored  shales,  with  occasional  very  thin  limestone 
layers,  and  the  same  greenish  argillitic  or  quartzitic  rocks  are  seen  here. 

The  purplish  shales,  with  their  thin  interbedded  limestones  just  men- 
tioned, remind  the  observer  of  the  Olenellus  Cambrian  rocks  found  in 
eastern  Massachusetts.  While  not  identifying  these  more  southern  expo- 
sures with  the  same  precise  horizon  northward,  the  writer  is  of  the  opinion 
that  eventually  the  purple  shales  of  Newport  Neck  and  Little  Compton  may 
prove  to  be  Cambrian  rocks. 

Farther  inland,  eastward,  the  exposures  consist  of  rock  varying  between 
quartzite  and  argillite,  with  abundant  parallel  shearing  planes,  often  show- 
ing the  effects  of  subseqiient  folding.  The  Cambrian  beds  in  Little  Comp- 
ton, east  of  the  shore  exposiu'es,  are  often  decidedly  quartzitic.  So  are 
also  some  of  the  shore  exposures.  It  is  not  unlikely  that  these  exposures 
include  more  than  one  horizon,  paleontologically  considered. 

'  Prof.  T.  N.  Dale  saw,  April  25,  1883,  iu  the  possession  of  Mr.  Coggeshall,  a  blacksmith  at  New- 
port, carbonaceous  shales  with  fragments  of  10  specimens  of  Aviculopecteu,  said  to  have  come  from 
Portsmouth  mine.  Sketches  of  these  fossils  were  submitted  to  Professor  Von  Zittel.  Their  impor- 
tance lies  in  the  fact  that,  if  authentic,  they  are  the  first  known  evidence  favoring  the  presence  of 
salt  water  during  Carboniferous  times  in  New  England. 

".S 


382  GEOLOGY  OF  THE  NARRAGANSETT  BASIN. 

The  wliitisli  rocks  between  the  conglomerate  ranges  in  the  great 
Paradise-Hanging  Rock  syncline  resemble  strongly  the  more  quartzitic 
exposures  away  from  the  shore,  east  of  the  Sakonnet  River. 

Quartzites  occur  well  exposed  (1)  west  of  Natick,  (2)  along  a  road  a 
short  distance  east  of  Natick,  (3)  southwest  of  the  town,  (4)  along  the 
northern  side  of  Bald  Hill,  (5)  on  a  knoll  directly  east  of  that  hill,  and 
elsewhere.  Possibly  various  exposures  west  of  East  Greenwich,  east  of 
Nonquit  Pond,  and  in  the  neighborhood  of  Tiverton  belong  here.  The 
quartzites  west  of  Natick  have  furnished  the  pebbles  in  the  basal  conglom- 
erate of  the  Carboniferous.  Pebbles  of  similar  character  occur  also  in  all 
the  overlying  conglomerates  as  far  up  as  the  Dighton  conglomerate. 

In  the  quartzite  pebbles  of  (1)  the  conglomerate  between  the  Saun- 
derstown  sandstone  series  and  (2)  of  the  Aquidneck  shale  series  on  the 
western  side  of  Prudence  Island  fossil  oboli  occur.^  They  are  found  also 
(3)  in  the  conglomerates  along  Newport  Cliffs,  and  (4)  in  the  coarse 
conglomerates  at  Eastons  Point,  (5)  in  the  Paradise  ridges,  (6)  along  the 
western  shore  exposures  of  the  Sakonnet  River,  and  also  (7)  east  of  that 
river  north  of  Tiverton  Four  Corners.  These  oboli  appear  identical  with 
fossils  from  the  passage  beds  between  the  Cambrian  and  Lower  Ordovician 
of  Great  Belle  Island  of  Newfoundland.  Hence  they  are  either  of  late 
Cambrian  or  early  Lower  Ordovician  age.  Notwithstanding  the  great 
abundance  of  quartz  pebbles  with  oboli,  however,  the  quartzite  containing 
oboli  has  never  been  found  in  situ.  It  may  be  that  the  Natick  quartzite  is 
a  remnant  of  the  old  Cambrian  quartzite,  but  since  it  contains  no  oboli  this 
can  not  be  determined.^ 

Considering  the  great  abundance  of  quartzite  material  in  the  coarse 
Purgatory  conglomerates,  the  quartzite  miist  have  once  occurred  in  consid- 
erable thickness  over  wide  areas.  It  is  not  improbable  that  the  quartzite 
once  occupied  a  considerable  part  of  the  area  now  occupied  by  pre- 
Carboniferous  granite.  Subsequent  erosion  appears,  however,  to  have 
effectually  denuded  these  areas  of  the  quartzite  beds,  excejjting  in  isolated 
localities,  as  at  Natick.     If  the  pebbles  were  derived  from  large  exposures 

'  The  following  species  have  so  far  been  discovered  in  the  quartzite  pebbles  derived  from  south- 
eastern Rhode  Island  and  Massachusetts;  Oholus  (Linguloholus)  affinis,  0.  (L.)  spissus,  and  Oholus 
{Lingulella)  rogersi. 

-Charles  D.  Walcott,  Brachiopod  fauna  of  the  quartzitic  pebbles  of  the  Carboniferous  conglom- 
erate of  the  Narragansett  Basin,  R.  I. :  Am.  Jour.  Sci.,  October,  1898,  3d  series,  A''ol.  VI,  p.  327. 


LITTLE  OOMPTON  AND  NEWPORT  NECK  SHALES.  383 

of  quartzite  lying-  as  far  north  as  Newfoundland  and  carried  southward  by 
glaciers,  the  absence  of  other  pre-Carboniferous  rocks  among  the  pebbles  is 
striking. 

LITTLE   COMPTON  AXD  ISTEWPORT  ISTECK  SHALES. 

The  distribution  and  general  characteristics  of  the  shales  in  western 
Little  Compton  and  along  the  western  shore  of  Newport  Neck  have  already 
been  sufficiently  described  in  Chapters  V  and  VI,  pages  281  and  316. 
The  shales  in  question  are  closely  related  lithologically,  and  are  evidently 
not  similar  to  any  kuown  Carboniferous  deposits  of  the  basin.  The  charac- 
teristic feature  is  evidently  the  presence  of  thin  layers  of  dolomitic  limestone 
in  both  areas,  and  the  presence  at  various  points  along  southern  Newport 
Harbor  of  quite  thick  beds  of  a  white  limestone,  weathering  to  brown.  The 
limestone  suggests  a  marine  origin  for  these  shales,  while  the  Carboniferous 
of  the  basin  is  evidently  a  fresh-water  deposit.  Not  a  single  marine  fossil 
has  so  far  been  found  in  the  Carboniferous  rocks,  and  no  trace  of  limestone 
beds  has  been  discovered  in  them.  (See  footnote  on  page  381.)  Under 
these  circumstances  the  Little  Compton  shales  and  the  Newport  Neck  sliales 
must  evidently  be  consigned  to  some  other  geological  horizon.  The  only 
other  horizons  so  far  determined  by  fossils  in  eastern  Massachusetts  are  the 
Olenellus  and  Paradoxides  Cambrian  and  the  Carboniferous.  The  Para- 
doxides  Cambrian  has  so  far  not  shown  the  presence  of  limestone  beds, 
nor  are  the  shales  ever  reddish.  The  Olenellus  Cambrian  shales  are,  how- 
ever, often  reddish,  often  include  very  thin  limestone  beds,  and  at  all  the 
localities  named  include  also  limestone  beds  6  to  8  inches  in  thickness. 
This  suggests  the  possibility  of  the  Little  Compton  and  Newport  Neck 
shales  being  of  Olenellus  Cambrian,  or  at  least  of  Cambrian  age.  Of 
coiu'se,  the  finding  of  fossils  will  afford  the  only  certain  means  for  iden- 
tifying the  horizons  of  these  beds. 

QTJARTZITES    OF    KATICK. 

The  quartzite  on  the  northern  side  of  Bald  Hill,  along  the  escarpment 
northwest,  west,  and  southwest  of  Natick,  and  at  various  points  along  tlie 
road  between  Drum  Rock  Hill  and  Natick,  has  already  been  described  in 
connection  with  the  general  geology  of  the  southern  part  of  the  Carbon- 
iferous basin.  These  quartzites  are,  however,  pre-Carboniferous.  The 
same  may  be  said  also  of  the  quartzites  occurring  from  Natick  northward 


384  GEOLOGY  OF  THE  NAREAGANSETT  BASIN. 

along  various  parts  of  the  escarpment  and  thence  up  the  Blackstone  Valley 
as  far  as  Ashton  and  Manville. 

The  question  as  to  the  geological  position  of  these  quartzites  is  very 
important,  but  at  present  is  without  a  solution.  On  lithological  grounds 
alone  they  might  be  considered  of  Cambrian  age,  but  there  is  little  real 
basis  for  such  a  determination.  Perhaps  the  best  reason  so  far  known  for 
considering  these  quartzites  as  of  Cambrian  age  is  the  abundant  occurrence 
of  Cambrian  quartzite  pebbles  in  the  Carboniferous  conglomerates  of  the 
Narragansett  Basin.  Quartzite  pebbles  occur  at  all  horizons,  from  the  con- 
glomerate beds  just  overlying  the  basal  arkoses  to  the  uppermost  layers  of 
the  coarse  Purgatory  conglomerate.  The  lowest  horizon  at  which  these 
quartzite  pebbles  contain  fossil  oboh,  however,  seems  so  far  to  be  in  the 
conglomerate  beds  between  the  Saunderstown  sandstone  and  Aquidneck 
shale  series  on  the  western  side  of  Prudence,  and  with  less  certainty  on  the 
western  side  of  Bristol  Neck  and  northwest  of  Riverside.  They  occur  in 
far  greater  abundance  in  the  coarse  Purgatory  conglomerate,  being  com- 
monly found  in  any  considerable  exposure  where  long-continued  search 
has  been  made  for  the  entire  length  of  Aquidneck  Island  and  the  eastern 
shore  of  the  Sakonnet  River.  They  occur  again  in  the  corresponding 
coarse  conglomerate  at  Dighton,  and  southwestward. 

A  few  of  the  localities  where  quartzite  pebbles  with  fossil  oboli 
have  been  found  in  situ  have  been  indicated  on  the  accompanjnng  geo- 
logical map.  These  fossil  oboli  belong  probably  to  some  late  Cambrian 
horizon.  Hence  the  quartzite  deposits  elsewhere  in  the  basin,  especially 
those  near  Natick,  in  which  we  are  most  interested,  may  also  be  of  late 
Cambrian  age. 

After  a  careful  comparison  of  the  quartzite  pebbles  in  the  quartzites  at 
Natick  and  elsewhere,  it  must  be  admitted,  however,  that  the  lithological 
resemblance  is  not  very  close.  The  varied  coloring  shown  by  different 
fossiliferous  quartzite  pebbles,  especially  a  rather  common  tint  of  faintly 
dark  blue,  altogether  fails  in  the  quartzite  exposures  so  far  examined.  The 
whiter  more  vitreous  quartzite  localities,  moreover,  do  not  present  the  same 
cleavage  as  the  whiter  fossil-containing  pebbles.  Furthermore,  when  the 
considerable  frequence  of  oboli-containing  pebbles  is  considered,  it  is  rather 
perplexing  to  find  the  quartzite  localities  in  question  apparently  without 
fossils. 


QUARTZITE  PEBBLES  WITH  OBOLI.  385 

While,  therefore,  the  suggestion  that  the  pre-Carboniferous  pebbles 
may  be  of  late  Cambrian  age  seems  to  be  the  only  one  possible  at  present, 
the  very  slender  basis  upon  which  this  suggestion  rests  should  not  be  left 
out  of  view.^ 


'  The  origin  of  these  fossiliferons  quartzite  pebbles,  as  well  as  the  question  of  their  age,  has  been 
discussed  by  Mr  Wood  worth  in  his  part  of  this  monograph.     It  seems  from  Dr.  Foerste's  presentation 
of  the  matter  that  no  considerable  importance  can  be  attached  to  the  suggestion  that  these  pebbles 
are  derived  from  the  Natick  or  other  known  quartzites  which  occur  in  the  basin. — N.  S.  S. 
MON  XXXIII 25 


CHAPTER    XII. 

THE  CAMBRIAN  STRATA  OF  THE  ATTLEBORO  DISTRICT. 

Among  the  most  interesting  results  of  the  examination  of  the  geology 
of  the  Narragansett  Basin  has  been  the  discovery  of  a  number  of  small 
Olenellus  Cambrian  exposures.  The  first  of  these,  locality  1,  directly  east 
of  Hoppin  Hill  (PL  XXVI),  and  a  mile  southwest  of  North  Attleboro,  was 
discovered  by  Prof.  N.  S.  Shaler  long  before  the  United  States  Geological 
Survey  began  its  work  here,  but  the  horizon  to  which  the  fossils  from  this 
locality  belonged  was  not  determined  until  the  publication  of  Bulletin  No. 
30  of  the  United  States  Geological  Survey,  by  Mr.  C.  D.  Walcott,  in  1886, 
made  more  widely  known  the  Olenellus  Cambrian  fauna  of  this  coiTntry. 

At  locality  1  were  found  Hyolithes  princepsf  and  HyolitheUiis  micansf 
in  considerable  abundance ;  a  small  form  of  Stenotlieca  nigosa  was  fairly 
common,  and  a  species  described  later  as  Salterella  curvata  was  also  numer- 
ous. The  operculum  of  Hyolithellus  has  so  far  not  been  found,  but  the 
general  Cambrian  facies  of  the  fauna  at  locality  1  was  readily  recognized 
as  early  as  1887.  In  the  fall  of  that  year  the  writer  was  sent  into  the  field 
to  collect  fossils,  and  the  result  was  the  discovery  of  locality  2,  a  third  of  a 
m.ile  north  of  locality  1 ,  which  has  furnished  almost  all  of  the  fossils  described 
from  the  Olenellus  Cambrian  of  Massachusetts,  and  of  locality  3,  a  mile 
directly  west  of  locality  2,  in  the  open  fields  west  of  a  little  stream,  and  at 
the  northern  end  of  a  long  farm  lane.  The  number  of  species  found  at 
locality  3  was  small,  but  it  added  to  our  information  regarding  the  areal 
distribution  of  the  Olenellus  Cambrian  in  this  part  of  the  field. 

The  results  of  these  investigations  were  published  as  an  appendix  to  a 
preliminary  report  on  the  geology  of  the  Cambrian  in  Bristol  County, 
Massachusetts,  in  1888.^  In  the  determination  of  species,  the  figures  of 
Bulletin  No.  30  (United  States  Geological  Survey)  were  followed  very 
closely.  When  widely  different  forms  were  figured  under  the  same  species, 
the  description  was  followed  as  well  as  possible.  The  collections  the 
writer  was  able  to  examine  at  that  time  afforded  but  little  assistance  in 

'Preliminary  descrij)tion  of  North  Attleboro  fossils,  by  N.  S.  Shaler  and  August  F.  Foerste: 
BuU.  Mus.  C'omp.  Zool.  Harvard  Coll.,  Geol.  Series,  Vol.  II,  pp.  27-41,  pis.  1-2,  Oct.,  1888. 


U-S. GEOLOGICAL  SURVEN 


MONOGRAPH     XXXIU.      PL.   XXVII 


& 


LEGEND 


r^ 


Carboniferous 


t^.ss.     (pt/ar/z/hc  sandstone 
g/:sh.     Green  shale 
r.s/j,     /fe  &  shale 


///.  Hyo/if^hellus 

yerf.      /erhical 
Cong/.   Con^Jomer^te 


r.  /.       /fed  /imestone 
fr/l.     Tri/obifes 
h,         Nyolifhes 


peb .        PebbJes 

/.noc/.     Limestone:  nodules 


SKETCH  MAP 

OP 


CAMBHJAN  FOSSIL  LO(.AJ.ITIES  I  AND  11 

SOTTTHVVEST  OK  NOIv'tj{  ATTLEBORO 


OAMBEIAN  DISTRICT  OF  NORTH  ATTLEBOEO.  387 

the  determination  of  species.  The  result  was  naturally  a  number  of  errors. 
The  worst  of  these  was  the  reference  of  a  small  head  of  some  species  of 
Olenellus  to  the  genus  Paradoxides.  The  specimen  found  was  a  cast  of  the 
lower  surface  of  the  chitinous  envelope  of  the  head,  and  apparently  showed 
facial  sutures,  the  nonexistence  of  which  in  the  genus  Olenellus  was  already 
suspected  at  that  time.  It  is  now  very  well  known  that  the  position  of 
facial  sutures  is  indicated  by  grooves  on  the  lower  surface  of  the  protecting 
envelope  of  the  head  (exoskeleton),  a  cast  of  which  could  erroneously  give 
the  idea  of  a  partial  separation  of  the  free  cheeks  at  the  facial  suture.  In 
spite  of  this  incorrect  reference  of  the  cast  in  question,  the  fauna  was 
recognized  as  being  of  the  Olenellus  Cambrian  horizon. 

In  consequence  of  the  discovery  of  an  Olenellus  Cambrian  fauna  in 
the  red  shales  and  limestones  southwest  of  North  Attleboro,  the  red  shales, 
sandstones,  and  conglomerate  farther  east,  and,  in  fact,  wherever  found  for 
miles  around,  were  considered  of  Cambrian  age.  Owing  to  their  general 
westward  dip  they  were  even  viewed  as  anteceding  the  fossiiiferous  beds. 
The  report,  however,  had  scarcely  been  pubhshed  when,  early  in  1889,  the 
writer  found  loose  bowlders  of  red  sandstone  with  well-preserved  specimens 
of  calamites  in  the  hills  southwest  of  the  southern  end  of  the  reservoir  pond 
south  of  North  Attleboro.  In  consequence  all  the  red  shales,  sandstones, 
and  conglomerates  just  described  as  Cambrian,  excepting  the  shales 
occupying  the  valleys  of  localities  1,  2,  and  3,  were  referred  to  the  Carbon- 
iferous. In  the  writer's  thesis,  On  the  Igneous  and  MetamorjDhic  Rocks  of 
the  Narragansett  Basin  (Harvard  Univ.,  1890),  these  red  phases  of  the 
Carboniferoiis  were  described  as  a  group  of  the  Carboniferous,  the  Wamsutta. 
After  this  thesis  had  been  presented,  in  the  spring  of  1890,  Cordaites  leaves 
were  found  in  sitti,  west  of  the  road,  two-thirds  of  a  mile  southwest  of 
the  reservoir  pond.  At  a  later  date  Mr.  J.  B.  Woodworth  discovered 
abundant  stems  of  calamites  in  an  exposure  on  the  north  side  of  the  road  to 
Attleboro  Falls,  about  two-thirds  of  a  mile  southeast  of  the  North  Attleboro 
post-office ;  and  finally,  in  1895,  the  writer  found  a  poorly  preserved  specimen 
uf  calamites  in  the  arkose  beds  in  the  northwestern  part  of  North  Attleboro, 
north  of  Division  street  ^ 

The  result  of  these  discoveries  has  been  of  considerable  importance  in 

'  It  should  be  noted  that  in  1880  Crosby  and  Barton  recognized  the  Carboniferous  age  of  the  red 
beds  in  the  Norfolk  County  Basin  and  inferred  from  this  a  similar  age  for  the  red  rocks  about  North 
Attleboro,  but  they  did  not  discover  the  factthataportionof  these  beds  were  of  Cambrian  age. — N.  S.  S. 


388  GEOLOGY  OF  THE  NARRAGANSETT  BASIN. 

arriving  at  a  correct  knowledge  of  the  litliological  characteristics  of  the 
OlenelKis  Cambrian  in  eastern  Massachusetts.  Instead  of  being  a  forma- 
tion in  which  sandstones  and  conglomerates  form  a  predominating  element, 
the  Olenellus  Cambrian  of  eastern  Massachusetts,  as  at  present  recognized, 
consists  chiefly  of  reddish  and  greenish  shales  and  slates  with  whitish  and 
reddish  layers  and  nodules  of  limestone.  Sandstone  beds  are  known  at 
almost  all  exposures,  but  form  only  a  very  unimportant  element  of  the 
Olenellus  Cambrian,  as  far  as  this  horizon  has  been  definitely  recognized. 

Some  sandstone  is,  for  instance,  found  associated  with  the  reddish 
shales  and  limestone  beds  discovered  in  1889  by  the  writer  at  locality  4, 
just  north  of  the  State  line,  a  short  distance  east  of  the  road  leading  from 
West  Wrentham  to  Diamond  Hill. 

North  of  Mill  Cove,  in  the  Boston  Basin,  the  Olenellus  Cambrian 
(fossils  discovered  by  the  writer  in  May,  1889)  consists  chiefly  of  reddish 
and  cherty  greenish  slate,  including  limestone  nodules,  and  a  few  limestone 
beds,  the  latter  containing  Hyolithes  communis  and  Hyolitliellus  micans. 

At  the  southern  end  of  Nahant  the  Olenellus  Cambrian  (fossils  first 
recognized  by  the  writer^  in  April,  1889,  but  previously  discovered  and  not 
identified  by  Prof  Alfred  C.  Lane  and  J.  Sears)  consists  of  cherty  greenish 
slate,  with  two  or  three  white  limestone  layers,  the  latter  containing  Hyolithes 
communis  and  a  small  form  of  Stenotheca  riigosa.  Near  the  southwestern 
angle  of  Topsfield  similar  cherty  greenish  slates  occm-,  the  fossiliferous 
limestone  being,  however,  hard  and  light  blue  in  color. 

At  Achelaus  Hill,  in  West  Newbury,  Mr.  John  Sears  reports  another 
instance  of  cherty  slates  similar  to  those  at  Nahant,  and  containing  similar 
fossils. 

No  great  masses  of  sandstone  and  conglomerate  have  so  far  been 
recoo-nized  as  belonging  to  the  Olenellus  Cambrian  horizon,  or  as  being 
closely  associated  with  the  same. 

CAMBRIAX  BROOK  LOCALITIES. 

LOCALITIES  1  AND  2,  SOUTHWEST  OF  NORTH  ATTLEBORO. 

A  great  mass  of  quartzite  on  the  southeastern  side  of  Hoppin  Hill 
mav  belong  to  the  Olenellus  Cambrian.  Fragments  of  reddish  shale  occur 
in  the  soil  farther  eastward. 

'  See  The  paleontological  horizon  of  the  limestone  at  Nahant,  Massachusetts:  Proc.  Boston  Soc. 
Nat.  Hist.,  Vol.  XXIV,  1889. 


CAMBRIAN  OF  NORTH  ATTLEBORO.  389 

At  localit}^  1,  just  north  of  the  road  leading  eastward  down  from 
Hoppin  Hill,  there  is  a  small  knoll,  composed  chiefly  of  shale,  more  greenish 
westward,  where  it  includes  a  few  thin  white  quartzite  layers,  strike  N.  10° 
E.,  dip  80°  W.;  reddish  eastward,  where  the  shale  includes  limestone  layers, 
pinkish  where  fresh,  red  where  strongly  weathered.     (Map,  PI.  XXVII.) 

In  the  limestones  were  found  the  following  fossils:  Stenotlieca  rugosa 
var.  i)aupet%  Pleurotomaria  (Baphistoma)  attlehoroensis,  Fordilla  troyensisf 
left  valve,  Hyolithes  princepsf  H.  hillingsi,  HyolUliellus  micansf,  Salter ella 
curvata.  Northeast  of  locality  1,50  feet,  are  found  some  very  small  exposures 
of  red  shale  with  limestone  layei's,  including  Agraulus  stremms,  strike  N.  10° 
E.,  dip  70°  W.  Farther  northward  1 00  feet,  a  little  east  of  north  from  locality 
1,  is  another  knoll  with  red  shale  on  the  eastern  side,  containing  red  lime- 
stone with  Hyolithes  and  Hyolithellus.  The  ridge  itself  is  composed  of 
greenish  and  reddish  shales  on  the  eastern  face,  and  greenish  shale  including 
thin  sandstone  and  quartzite  beds  along  the  middle  and  western  sides. 

About  150  feet  north  of  the  last-mentioned  knoll,  or  340  feet  north 
of  locality  1,  reddish  shale,  abundantly  cleaved  in  various  directions,  occurs 
just  west  of  the  stream,  and  another  exposure  occurs  near  by  on  the  eastern 
side  of  the  stream.  West  of  these  localities  green  and  red  shales  occur, 
also  much  cracked;  50  feet  farther  north,  and  again  110  feet  farther  north, 
limestone  bowlders  occur.  Another  limestone  bowlder  is  found  about  50 
feet  west  of  the  last-mentioned  bowlder  and  about  525  feet  a  little  west  of 
north  of  locality  1. 

About  560  feet  almost  directly  north  of  locality  1  and  just  south  of  a 
small  stream  red  shale  is  found  including  thick  red  limestone  beds  in  almost 
vertical  position.  Thirty-five  feet  northwest  of  the  same  red  shale  occurs; 
50  feet  directly  westward  occurs  limestone  containing  Hyolithes  and  Hyoli- 
thellus, strike  N.  50°  E.,  dip  vertical. 

Thirty  feet  northwestward  is  the  beginning  of  a  set  of  greenish  shales 
including  numerous  quartzite  layers,  the  most  eastern  one  12  inches  thick, 
the  intermediate  ones  a  few  inches  in  thickness,  the  most  western  layer 
nearly  2  feet  thick  and  white  in  color,  strike  N.  21°  E.,  dip  60°  E. 
About  25  feet  noi'theast  of  this  most  western  exposure  a  similar  thick 
quartzite  layer  with  a  similar  strike  occurs. 

About  110  feet  east  of  the  last-mentioned  quartzite  exposure,  on  the 
northern  side  of  the  small  stream  already  mentioned,  a  series  of  red  shale 


390  GEOLOGY  OF  THE  NAEEAGANSETT  BASIN, 

ridges  begins,  trending  N.  20°  E.  for  a  distance  of  200  feet.  Just  north  of 
a  wood  road  the  shales  strike  N.  30°  E.,  with  a  dip  of  85°  to  vertical.  The 
shales  contain  nodules  of  limestone  which  have  yielded  a  few  casts  of 
Agraulus  stremms. 

The  ridges  above  described  terminate  at  a  point  just  south  of  the  open 
fields.  About  300  feet  northwestward,  near  the  western  edge  of  the  open 
fields,  occurs  locality  2.  It  is  a  knoll  trending  N.  15°  W.  and  consisting 
chiefly  of  reddish  and  greenish  shales ;  lying  upon  the  top  and  western  side 
of  the  knoll  are  great  limestone  blocks  whose  position  in  the  section  can 
not  be  accurately  determined,  but  which  have  furnished  all  the  fossils  cited 
as  coming  from  locality  2.  The  bowlders  seem  to  belong  to  layers  in  the 
immediate  vicinity,  but  to  have  been  broken  up  by  the  evidently  strong 
folding  and  shearing  of  the  Cambrian  strata  in  this  region. 

The  following  fossils  have  been  found  at  locality  2:  Oholella  atlantica 
Walcott,  figured  but  not  named  in  our  report;  Oholella  crassa  Hall,  Scenella 
reticulata  Billings,  Stenotheca  curvirostra  S.  &  F.,  Stenotlieca  rugosa  var. 
ahrupta  S.  &  F.,  Platyceras  primcBvum  Billings,  Hyolitlies  americanus,  Hyoli- 
tlies  communis  vai*.  emmonsi  Ford,  Hyolitlies  quadricostatus  S.  &  F.,  Microdis- 
ciis  hellimarginatus  S.  &  F.,  M.  lohaius  Hall,  Olenellus  iimlcotti  S.  &  F. 
(probably  a  young  form  of  some  known  species),  PtycJioparia  attleboro- 
ensis  S.  &  F.  (probably  the  young  form  of  some  species  of  trilobite), 
Agraulus  stremms  f  Billings. 

Northwest  of  locality  2,  on  the  other  side  of  a  fence,  is  another  knoll, 
trending  N.  23°  E.,  consisting  chiefly  of  reddish  and  greenish  shales,  but 
containing  on  the  west  side  a  few  nodules  of  limestone  which  have  aff'orded 
Hyolithes  and  fragments  of  Agraulus. 

There  is  a  similarity  of  trend  between  the  Cambrian  deposits  at  locality 
1  and  immediately  northward,  and  at  the  margin  of  the  granite  hill  imme- 
diately to  the  westward  of  it.  This  is  also  true  in  a  measure  of  the  outcrops 
south  of  the  stream  about  500  feet  north  of  locality  1,  and  600  feet  south  of 
locality  2,  where  the  quartzite  shale  and  limestone  beds  strike  northeastward, 
while  the  granite  hill  on  the  west  seems  to  make  a  similar  deflection. 
Again,  at  locality  3  and  northwestward,  the  Cambrian  strata  strike  north- 
westward, apparently  following  the  general  trend  of  the  eastern  margin  of 
the  granite  hill. 

Quartzite  occurs  at  the  southeastern  angle  of  Hoppin  Hill,  just  north- 


OAMBKIAN  OF  NOETH  ATTLEBORO.  391 

west  of  locality  1,  in  the  underbrush,  and  about  halfway  between  locali- 
ties 1  and  2  on  the  west  side  of  the  set  of  exposures  already  described. 
The  temptation  is  very  strong  to  consider  the  quartzite  and  the  associated 
green  shales  as  forming  the  lowest  beds  of  the  series  actually  exposed. 
The  limestone  beds  immediately  toward  the  east  of  the  green  shale  and 
associated  quartzite  layers,  containing  Hyolithes  and  Hyolithellus  chiefly, 
at  locahty  1,  and  again  just  east  of  the  green  shales  and  sandstones  halfway 
between  localities  1  and  2,  could  then  be  considered  as  forming  an  immedi- 
ately overlying  horizon,  while  the  beds  still  farther  eastward,  containing 
frequent  trilobite  remains  (Agraulus  strenuus),  might  be  considered  as 
belonging  to  a  still  higher  horizon.  This  would  suggest  that  locality  2 
belongs  to  a  horizon  slightly  higher  than  locality  1. 

About  700  feet  north  of  locality  2  is  found  a  granite  boss,  the  northern 
margin  of  which  extends  northeastward,  forming  a  steep  wall.  On  the 
northern  side  of  this  wall,  in  close  contact  with  the  granite,  a  small  exposure 
of  red  shales  was  unearthed  in  1887. 

Red  shales  also  occur  at  various  points  on  the  eastern  side  of  the  valley 
in  which  localities  1  and  2  occur.  The  general  conclusion  is  that  the  val- 
ley as  far  as  described  is  underlain  altogether  by  Olenellus  Cambrian  rocks. 

The  western  side  of  the  valley  is  bordered  by  the  HopjDin  Hill  granite 
boss.  On  the  northeastern  side,  toward  North  Attleboro,  occurs  the  second 
boss,  already  described,  and  along  the  remainder  of  the  eastern  side  of  the 
valley  the  Olenellus  Cambrian  is  overlain  by  the  Carboniferous.  The  most 
southern  Carboniferous  exposure  north  of  the  east-west  Hoppin  Hill  road 
and  east  of  the  Cambrian  area,  strike  N.  10°  W.,  dip  vertical,  occurs  on 
the  hillside,  only  325  feet  north  of  the  road  leading  east  down  from  Hoppin 
Hill.  Another  exposure  is  250  feet  north;  a  third  is  115  feet  north,  strike 
N.  40°  E.;  a  fourth  is  75  feet  north,  strike  N.  15°  E.,  dip  steep  west.  All 
of  these  exposures  are  conglomerates,  in  which  the  pebbles  consist  of  a  hard 
glassy  quartzite. 

South  of  the  Hoppin  Hill  road  leading  eastward  are  several  additional 
exposures  of  Carboniferous  conglomerate  and  shale  on  the  east  side  of  the 
Olenellus  Cambrian  valley. 

The  construction  of  the  new  railroad  through  the  western  part  of  the 
village  of  North  Attleboro  has  disclosed  a  series  of  red  shales  south  of 
the  depot,   as  far  as  the   bend  of  the  road  toward  the  southeast.     The 


392  GEOLOGY  OF  THE  NAEEAGANSETT  BASIN. 

geological  position  of  these  shales  is  unknown.  Next  the  depot  and  north- 
ward occur  exposures  of  arkose,  undoubtedly  Carboniferous.  It  is  possible, 
however,  that  the  red  shales  in  question  still  belong  to  the  Olenellus  Cam- 
brian, which  is  here  again  overlain  by  the  Carboniferous. 

VALLEY  OF  LOCALITY  3. 

The  road  across  Hoppin  Hill  leads  from  locality  1 ,  first  westward,  then 
southwest,  nearly  south,  then  again  west  until  a  small  stream  is  crossed. 
A  short  distance  west  of  the  stream  is  a  house.  Along  the  farm  lane  to  the 
northward  red  limestone  bowlders  apjDear  in  the  fence  wall  on  the  left  side  of 
the  way.  The  bowlders  increase  in  frequency  as  the  end  of  the  lane 
is  approached.  At  the  northeastern  end  of  the  field,  just  west  of  the 
northern  end  of  the  lane,  red  shale  is  exposed  in  the  soil.  The  limestone 
bowlders  probably  belong  in  situ  somewhere  among  the  red  shales  of  the 
vicinity,  but  at  the  present  time  their  precise  location  can  not  be  determined. 

The  above-mentioned  limestone  bowlders  have  furnished  the  following 
fossils:  Oholella  crassa,  Scenella  reticulata,  Stenotheca  rugosa  var.  ahrupta, 
Hyolitlies  communis,  possibly  also  H.  communis  var.  emmonsif  Microdiscus 
bellomarginatus,  and  Agrauliis  strenuus.  Judging  from  the  fauna  alone,  local- 
ity 3  belongs  to  the  horizon  of  locality  2,  rather  than  to  that  of  locality  1. 
No  quartzitic  layers  have  been  observed  in  this  valley,  and  the  actual  expo- 
sures, as  already  stated,  are  confined  to  red  shales.  The  Olenellus  Cambrian 
deposits  of  this  valley  are  bordered  on  the  east  by  the  granite  of  Hoppin 
Hill.  Toward  the  northwest  occur  several  granite  exposures,  eAndently 
connected  beneath  the  soil,  and  trending  approximately  north  and  south. 
Directly  west  there  are  no  exposures,  but  if  there  be  any  Cambrian  in  this 
direction  it  is  probably  ovei'lain  by  the  Wamsutta  Carboniferous,  which  is 
known  to  occur  considerably  farther  westward  in  the  valley  of  Abbotts 
Run.  In  this  direction  ai'kose,  possibly  near  the  base  of  the  Carboniferous, 
occurs  about  a  mile  north  of  locality  3,  on  the  road  from  North  Attleboro 
to  Ai'uolds  Mills,  and  is  quite  abundant  eastward  as  far  as  North  Attleboro. 
Wamsutta  Carboniferous  conglomerate  occurs  also  a  mile  and  a  half  south 
of  locality  3,  apparently  covering  the  Olenellus  Cambrian  in  this  direction. 
Red  shales  occur  at  various  points  west  and  southwest  of  South  Attleboro, 
but  so  close  to  Wamsutta  Carboniferous  exposures  that  it  is  impossible  for 
the  present  to  consider  them  as  of  Olenellus  Cambrian  age.     It  may,  how- 


CAMBRIAN  NORTH  OF  DIAMOND  HILL.  393 

ever,  be  worth  while  to  call  attention  to  their  distribution  as  recorded  in  the 
section  of  this  report  which  has  been  prepared  by  Mr.  Woodworth. 

LOCALITY  4,  NORTHEAST  OF  DIAMOND  HILL. 

Along  the  road  from  Diamond  Hill  northward  to  West  Wrentham 
exposures  of  granite  are  met  almost  immediately  on  crossing  the  State 
line  fi-om  Rhode  Island  into  Massachusetts.  After  following  the  southern 
margin  of  the  granite  hill  eastward  along  the  base  of  the  hill  for  a  distance 
of  several  hundred  feet,  a  change  in  direction  of  the  border  toward  the 
northeast  takes  place.  Here  a  number  of  red  limestone  bowlders  are  found 
on  the  hillside.  Toward  the  brow  of  this  hill  there  is  a  fair  exposure  of  red 
shales  dipping  at  a  high  angle  westward  and  striking  east  of  north.  West 
of  these,  quartzitic  beds  probably  occur,  as  is  shown, by  fragments  in  the 
soil  and  on  the  hillside. 

The  loose  bowlders  on  the  hillside  evidently  are  almost  in  situ  and 
contain  Hyolithes  princeps  f  and  Hyolithellus  micans  f ,  siiggesting  nearer  rela- 
tion with  locality  1.  From  the  top  of  this  part  of  the  hill  it  is  a  distance 
of  about  100  feet  to  the  border  of  the  granite  mass  forming  the  main  body 
of  the  hill.  Along  the  brow  of  the  hill  westward  the  granite  is  seen  to 
inclose  long  thin  layers  of  an  argillitic  purplish  or  brownish  rock,  which 
may  possibly  be  fragments  of  Olenellus  Cambrian  shale  hardened  by  meta- 
morphism.  It  is  impossible  to  determine  from  these  inclusions  whether  the 
granite  of  these  regions  is  to  be  considered  as  pre-  or  post-Cambrian  in  age. 
If  the  fragmental  inclusions  referred  to  be  Olenellus  Cambrian  shales  the 
granite  must  evidently  be  considered  as  post-Cambrian.  Post-Cambrian 
granites  are  well  known  in  the  Quincy  region  in  eastern  Massachusetts. 


MAPS    AND    SECTIONS. 

The  uncertainty  which  accompanies  many  of  the  views  regarding  the 
geological  stiiicture  of  the  lower  Narragansett  Basin  is  largely  due  to  the 
fact  that  the  greater  part  of  the  area  is  covered  by  glacial  di-ift  and  sand 
plains  or  concealed  by  the  water  of  the  many  arms  of  the  bay.  This  is 
well  brought  out  by  the  map,  which  indicates  the  position  of  almost  all 
outcrops  of  any  value  for  geological  purposes.  Moreover,  the  outcrops  are 
frequently  scanty  or  absent  at  the  very  horizons  where  it  is  exceedingly 
desirable  to  have  them  in  order  to  determine  the  question  of  the  succession 
and  the  equivalence  of  the  rocks.  It  was  necessary  on  tliis  account  to 
leave  some  areas  without  other  indication  than  the  color  for  the  general 
Carboniferous.  The  boundaries  of  some  of  the  divisions  recognized  may 
eventually  have  to  be  somewhat  shifted,  as  sewers,  ditches,  and  cellars 
expose  rocks  now  hidden  from  sight. 

.Moreover,  in  order  to  present  anything  in  the  nature  of  a  section 
across  strata,  it  was  necessary  to  generalize  the  interpretation  of  outcrops. 
A  reference  to  the  map  will  usually  indicate  the  extent  to  which  this  has 
been  done. 

There  is  perhaps  little  doulDt  that  both  the  Kingstown  sandstones  and 
the  Aquidneck  shales  have  been  considerably  folded.  Tliis  must  certainly 
be  true  of  the  Kingstown  sandstones  between  Wickford  and  Potowomut 
Neck,  and  also  of  the  Aquidneck  shales  from  Coddington  Cove  to  Black 
Point.  But  unfortunately  we  have  so  far  no  indications  as  to  the  precise 
locations  of  any  of  the  synclines  or  anticlines  in  tliis  system  of  folding.  It 
therefore  seemed  impossible  to  introduce  folds  into  the  section,  offering 
jjossibly  a  source  of  even  greater  en-or  than  if  these  indications  were 
omitted,  but  the  general  necessity  of  assuming  folding  was  brought  out 
clearly  in  the  text.  Actual  exposures  are  shown  in  the  sections  by  solid 
lines,  while  inferences  as  to  the  continuation  of  these  exposures  beneath 
the  soil  and  the  probable  attitude  of  strata  where  there  are  no  exposures 
are  indicated  by  dotted  lines. 


U.S. GEOLOGICAL  SURVE\ 


MONOGRAPH     XXXIII.    PL.  XXVIII 


Dips  probably  ht¥  e^s/  r 


Th/ssechon ^ffempfs/ocorre/ste  fhechiefei^oost/r^si^ffh simifar/i^ho/cg/cafcheracfen^ 


SECTIONS     IN     THE    NARRAGANSETT    BAY    REGION 


U.S-GEOLOGICAL  SURVEY 


MONOGRAPH    XXXIII.     PL.   XXIX 


■Si  5 


?  s- 


- — ^^ 

4 

1 

~^ 

Vt;!'^^^'^^-^ 


l/ff/e  Compfon  shale 


SECTIONS     IN     THE    NARRAGANSETT    BAY    REGION 


us. GEOLOGICAL  SURVEN 


MONOGRAPH     X/XII 


/felahonofCarbonJape^m  Granifenotceriain 


Purgatory  coarse  c 


7  eha/e  So  -Jooft 


Acjufdneck  shales.  2?oo'J5oof}' 


Prudence    Island 
Coaly  Shaie  Joo  -  ISoft     Co/^/omeraie  i-coalysha(e 


O^ooTerate.ffeclfyf^.  r 


Kingstotvn  sandstones  HSoo  feet 


Basal  ar/ft>s€  5o~f5off. 


"^  1 

CarSom'fierous 

% 
J 

1 

^- 

1 

!,}  1 

iTnpinnnnnnn^nnriinTiii 

""    Cambrian 

^- 

^i'^ 

-,-J.Jm,'_-',  \'- 

:.;.•% 

„  Carboniferous 

SECTIONS    IN     THE    NARRAGANSETT    BAY    REGION 


2 

< 

W 
^  ■ 

55 


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^" 

wg 
^^ 

OS 

as 

o    = 

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^|-_  is 

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-=i=    is 


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INDEX. 


J^, 


Page. 


AbingtoD,  Mass.,  fault  in 129 

Abington  quadrangle,  Coal  Measure  beds  in 193-194 

Achelaus    Hill,  West    Newbury,  Mass.,  Cambrian 

Tocksat 388 

Ackno-wledgments  to  coadjutors 211 

Agraulus  strenuus,  occurrence  of 389,  390,  391,  392 

Alethopteris,  occurrence  of 181 

Allegheny  Mountains,  age  and  character  of 10 

Almys  Pond,  E..  I.,  granite  near 316 

Amphibolite  in  dike  at  Lincoln,  character  of 108 

Analyses,  coals 83, 161, 191 

limestone 150 

Annularia,  occurrence  of 191,285 

Annularia  longifolia,  occurrence  of 268,  320, 321 

Anthracomartus  woodruffi,  occurrence  of 202 

Appalachian   Mountains,  ancient   mountain    range 

east  of  and  parallel  to 11 

difference  in  degree  of  erosion  in  eastern  and 

western  parts  of 40-46 

difference  in  form    of   folds  on  east  and  west 

sides  of 12-13 

folds  of 10-13 

form  and  origin  of  basins  east  of 13 

Aquidneck  Coal  Company,  operations  of 207 

Aquidneck  Island,  K.  I.,  Aquidneck  shales  on 252-358 

coal  beds  of 79,  80 

coal  mine  in 207 

folds  on 345 

granite  area  on 273-274 

rocks  of 284-330 

suggested  esploration  for  coal  on 85 

Aquidneck  shales,  area!  distribution  of 361 

debatable  question  as  to  inclusion  of  Kingstown 

series  in xviii-xix 

equivalence  of  Kingstown  sandstones  and 361-363 

folders  of 394 

fossils  of 363 

geologic  equivalents  of 358-359 

occurrence  and  character  of 348-363 

table  showing  geologic  place  and  equivalents  of. .         134 

thickness  of 352-354,  357-358,  359 

view  of  wave-cut  bench  in 352 

view  showing  fretwork  feathering  of 362 

Arkose,  occurrence  and  significance  of 50-55 

Ashton,  R.  I.,  Cumberland  quartzite  at 106 

Ashton  schists,  occurrence  and  character  of 107 

Asterophyllites,  occurrence  of 174, 191 

Asterophyllites  equisetiformis,  occurrence  of 168, 204 

Atlantic  coast,  basins  of  sedimental  depression  on..       13-15 

Carboniferous  basins  of 38-39 

character  and  extent  of  erosion  on 44-46 

geologic  history  of  shore  land  basins  of 30-36 


Page. 

Attleboro,  Mass.,  analysis  of  limestone  from 150 

Carboniferous  beds  in 175--180 

sections  at  and  near 153, 176, 177, 182 

syncline  at 179-180 

view  of  Carboniferous  sandstones  at 176 

views  of  conglomerate  at  and  near 176, 184 

view  of  pebbles  from  Dighton  conglomeratenear.  186 

view  of  raindrop  imprints  on  rocts  near 178 

view  of  ripple-marked  sandstones  near 178 

Attleboro  district,  Cambrian  strata  and  fossils  of  - . .  386-393 

Attleboro  sandstone,  occurrence  and  character  of . . .  151-152 

table  showiug  geologic  place  and  equivalents  of.  134 

Arachnida,  occurrence  of 202' 

Archean  rocks,  occurrence  and  character  of 114-118 

Arkose,  occurrence,  character,  and  significance  of...     50-58, 
135-139,  284-286,  375-380 

Arnolds  Mills,  R.I.,  granite  porphyry  at 117 

geologic  section  of  beds  near 157 

J3. 

Barbers  Height,  E.I. , Kingstown  series  at 334 

Barton,  G.  H.,  acknowledgments  to 211 

cited  as  to  anticlinal  structure  of  Hanging  Rock 

district 299 

cited  on  .structure  of  Hanging  Rock  ridge 367 

Basal  conglomerates,  occurrence  of 375-380 

Base-leveling,  general  cliaracter  and  extent  of 47-49 

marine  actions  contributory  to 76 

Beacon  Hill,  R.  I.,  conglomerates  at  and  near.  304,  305,  369-370 

Beaver  Head,  R.  I.,  rocks  of 338-339 

Bibliography  of  the  Cambrian  and  Carboniferous 

rocks 212-214 

Bishop  Rock,  R.  I.,  shales  near 305-306 

Black  Point,  R.  I.,  rocks  near 290-293,334 

Blactstone  Coal  Company,  operations  of 206 

Blackstone  River,  folded  and  faulted  Carboniferous 

shales  on 162 

Blackstone  series,  geologic  place  of g 

occurrence,  character,  and  relations  of 104-109 

Blake  Hill,  Mass. ,  fault  block:  at 180 

faults  near 183-184 

thrust  plane  at 133 

Blattinarise,  occurrence  of 203 

Bogs,  agricultural  utilization  of 78-79 

Bonnet  (The),  R.  I.,  Kingstown  series  at...  333,334,337,344 
Boston  Basin,  Mass.,  geologic  history  of 13-15,24-25 

erogenic  action  in 24-25 

Boston  Neck,  R.  I.,  faulting  near 377 

Kingstown  series  at '. 333 

Bowlder  clay,  thickness  and  character  of 69-70 

Bowlder  trains,  length  of 71-72 

Brachiopods,  Cambrian,  occurrence  of 109,110.111,112 

395 


396 


Il^DEX. 


Braytons  Point,  Mass.,  shales  with  fossil  plants  at. .         268 

Brentons  Cove,  E.  I.,  rocks  near 316,317 

Bridgewater,  Mass.,  Carboniferous  beds  near 192-193 

coal  beds  in 205 

Bristol,  E.  I.,  coal  beds  at -,•  79-80,206 

fossil  insects  from 202,201 

Bristol  Neck,  E.  I.,  Carboniferous  and  granitic  rocks 

on 261-263,  343-344,  351-352 

synclinal  fold  near ^^^ 

Brockton,  Mass.,  Carboniferous  beds  near 192-193 

Browns  Point,  E.  1.,  rocks  at  and  near 281-283,286 

Burr,  H.  T.,  cited  1*'' 

Butts  Hill,  E.I.,  rooks  at  and  near 327,328 

C. 

Calamites,  occurrence  of 170, 174, 191,321 

Calamites  suokovii,  occurrence  of 165 

Cambrian  rocks,  bibliography  of 212-214 

map  showing  distribution  of  pebbles  from 110 

origin  of  red  color  of 62-63 

pebbles  and  fossils  from 109-113 

Cambrian  rocks  and  fossils,  occurrence  of 381, 

382,  383,  384,  385,  386-393 

Canton,  Mass.,  gabbro  and  granitite  at 118 

Canton  Junction,  Mass.,  gabbro  and  granitite  at 118 

Carboniferous  basin,  boundary  of 124-130 

Cambrian  and  other  inlying  areas  in 130-131 

conditions  of  strata  in 119 

features  of H9-132 

features  of  faults  on  border  of 132 

maps  and  sections  of 121, 122, 123 

Carboniferous  clay  slate,  fresh-water  origin  of 202 

Carboniferous  conglomerates,  character  of 64-67 

glacial  pebbles  derived  from 70-71 

Carboniferous  period,  development    of  fresh-water 

basins  on  Atlantic  coast  during 38-39 

geologic  conditions  immediately  preceding 8-9, 13 

Carboniferous  rocks,  basins  in 12 

bibliography  of 212-214 

folds  and  fractures  limited  to 20-21 

line   of  separation   between   preCarboniferous 


Now  England  areas  of 12 

occurrence,  character,  and  thickness  of- .  119-201, 208-210 

origin  of  red  color  of 62-63 

original   distribution   in    eastern    Appalachian 

coalfield 38-39 

original  extent  of 40 

precise  age  of 36-37 

series  underlying 104-113 

table  siiowing 134 

Carboniferous  sandstones,  view  of 1S6 

Carrs  Point,  E.  1.,  rocks  near 319 

Case's  coal  mine,  operations  at 206-207 

Caseys  Point,  E.  I.,  Carboniferous  rocks  near 248 

Castle  Hill,  E.  I.,  rocks  at 31" 

Central  Falls,  E.  I.,  rocks  of  Wamsutta  group  near. .  147 

Chace,  G.  F.,  record  of  artesian  well-boring  furnished 

by 108 

Chartley  quarry,  section  in 19*^ 

Chemical  analyses.    [See  Analyses.) 

Churchs  Point,  E.  I.,  Carboniferous  rocks  near 283 

Clark,  E.  F.,  fossil  plants  collected  by 203-204 

Clay,  bowlder,  occurrence  of 69-70 

Clay  slate  (Carboniferous),  fresh-water  origin  of 202 


Clump  Eocks,  Carboniferous  rocks  atandnear 244-245 

Coal,  analyses  of 83,161.191 

economic  value  of 80-88 

occurrence  and  character  of  beds  of 79-88, 

161,  169, 171, 176, 182,  189, 190,  191,  192, 
198,  205-207,  321,  322,  323,  324,  325,  372 

places  for  exploration  for 85-88 

profitless  exploitation  of  beds  of xix 

suggested  method  of  prospecting  for 207-208 

Coal  field  of  Eastera  Appalachians,  original  distribu- 
tion of 38-39 

Coal  Measures,  areas,  exposures,  subdivisions,  thick- 
ness, and  general  features  of 159-201 

Coastal  erosion,  character  and  extent  of 44-46 

Coasters  Harbor  Island,  arkose  of 380 

Carboniferous  rocks  ou. 306-307,  370,  371 

contact  line  of  Carboniferous  and  pre-Carbonifer- 

ous  rocks  on 308-309 

Cobb,  Collier,  cited  on  increase  of  metamorphism 

with  increase  of  depth  of  strata 191 

cited  on  King  Mountain,  !N.  C 44 

record  of  boring  at  Portsmouth,  E.  I.,  examined 

by ■ 321 

Cochesett  Station,  Mass.,  section  near 192 

Cockroaches,  Carboniferous,  occurrence  of 202 

Coddington  Cove,  E.  I.,  rocks  near 319 

Coddington  Neck,  K.  I.,  shales  on 305 

Coloration  of  rocks,  causes  of 115 

Coman,  C.  "W.,  acliuowledgments  to 211 

Compression  of  rocks  by  lateral  strain,  evidence  of.      17-18 

diagram  showing  conditions  of 19 

Conanicut  Island,  E.  I.,  Aquidneck  shales  on 349 

arkose  of 380 

Carboniferous  rocks  of 308,  339 

folding  of  Kingstown  series  on 345 

fossil  plant  localities  on 347 

geologic  features  of 228-235 

Kingstown  series  on 339 

probable  folding  in 340-341 

thickness  of  arkose  on 380 

Conglomerates,  occurrence  and  character  of 55-61, 

64-67,  375-380 

glacial  pebbles  derived  from 70-71 

origins  of 55-59 

record  value  of 59-61 

Connecticut  Basin,  geologic  history  of 13-15,  23-24 

erogenic  action  in 23-24 

Cordaites,  occurrence  of 170, 191.387 

Corys  Lane,  section  near 320-321 

Cranston,  E.  I.,  analysis  of  coal  from 161 

bed  of  limestone  in 108 

coal  beds  at 79,80,206 

coaly  shales  at 335 

fossil  insects  from 202, 203 

Kingstown  series  at 335-336,  342 

Cranston  beds,  occurrence  and  character  of 159-164 

table  showing  geologic  place  and  equivalents  of.  134 

Croll,  James,  cited 64 

Crosby,  "W.  O.,  cited  as  to  anticlinal  structure  of 

Hanging  Eock  district 299 

cited  on  coloration  of  rocks 115 

cited  on  Montalban  rocks 104 

cited  on  structure  of  Hanging  Eock  ridge 367 

features  of  geologic  map  prepared  by 125 

Crosby,  W.  O.,  and  Barton,  G.  H.,  cited  on  boundary 

of  Carboniferous  basin 125, 127 


INDEX. 


397 


Page. 
Crosby,  W.  0.,  and  Barton,  G.  H.,  cited  on  Carbon- 
iferous age  of  red  beds  about  North  Attle- 

boro 141,387 

cited  on  dike  rocks  of  Paradise  liock— Hanging 

Kock  region 301 

cited  on  Primordial  rocks 109 

Cumberland, R.I. ,  coal  mine  in 206 

conglomerate  beds  at 140 

iron  ore  at 89 

Cumberland  Hill.  R.  I.,  bowlder  train  at 72 

Cumberland  quartzites,  character  and  occurrence  of.  106-107 
Current  and  surf  action,  character  and  extent  of  ero- 
sion by 76 

D. 

Dale,  T.  Nelson,  cited  as  to  anticlinal  structure  of 

Hanging  Roct  district 299 

cited  as  to  unconformity  between  Cambrian  and 

Carboniferous 308 

cited  on  fern  impression  in  shale  on  Conanicut 

Island 339 

cited  on  obscuration  of  rock  relations  by  fault- 
ing   360 

cited  on  occurrence  and  position  of  conglomer- 
ates at  Newport 373 

cited  on  occurrence  of  coal  seams  and  coal  plants 

in  excavations  at  Newport 372 

cited  on  occurrence  of  quartz-porphyry  on  New- 
port Neck 316 

cited  on  possible  unconformity  between  Carbon- 
iferoxis    arkose    and    Cambrian    shale  near 

Sachueat  Point 287 

cited  on  rocks  of  Paradise  Rock,  Hanging  Rock 

region 303 

cited  on  salt-water  fossils  in  Carboniferous  shales  -  381 

cited  on  structure  of  Hanging  Rock  ridge 367 

cited  on  thickness  of  shales  at  Eastons  Point. . .  358 

early  geologic  map  prepared  by 133 

fossil  fern  locality^  Conanicnt  Island,  discov- 
ered by 347 

Dana,  J.  D.,  cited 127 

Davis,  W.  M.,  cited  on  formation  of  faults  in  the  Con- 
necticut Basin 23 

Davisville,  R.  I.,  Carboniferous  rocks  near 251 

Dedham  quadrangle,  Carboniferous  beds  of 187-193 

Denudation,  difficulties  of  stratigraphic  determina- 
tion occasioned  by 101-102 

Deposition,  cycles  of 49-50 

Devils  Foot  Ledge,  R.  I.,  view  showing  cross  stratifi- 
cation in  pebbly  sandstone  at 248 

view  showing  sandstone-gneiss  at 334 

Diabase,  occurrence  of 152-153 

relations  of  felsite  and 154 

view  of  dikes  of 152 

Diamond  Hill,  R.  I.,  Cambrian  rocks  and  fossils  of . .  393 

granite-porphyry  and  quartz  at 117, 118 

quartz  mass  at    155 

Dictyopteris  scbeuchzeri,  occurrence  of 204 

Dighton  conglomerate,  views  of 184 

view  of  pebbles  from ^,  ige 

Dighton  conglomerate  group,  beds  of 184-187 

table  showing  geologic  place  and  equivalents  of.  134 

Dikes  and  dike  rocks,  occurrence  of 27-29, 152-153 

Diorite,  occurrence  of 118 

Distortion  of  pebbles  and  fossils  by  compression 18 


Dodgeville,  Mass.,  conglomerate  beds  near 175-176 

Dumpling  Rock,  Conanicut  Island,  character  of 234-235 

Dutch  Island,  R.  I.,  geologic  features  of 227-228,  337-338 

E. 

East  Foxboro,  Mass.,  gabbro  and  granititeat 118 

East  Greenwich,  R.  I.,  Carboniferous  rocks  near.  251, 252-253 
East  Providence,  R.  I.,  cross  section  near 168 

Tenmile  River  beds  at 164-165 

Eastons  Point,  R.  I.,  rocks  at  and  near  .     294-295,  357,  365,  372 

Eastons  Pond,  conglomerates  near 303,  370, 371 

Economic  resources  of  the  basin *. 77-90 

Emmons,  A.  B.,  analyses  of  coal  cited  from 191 

cited  on  fraudulent  coal  core  from  boring  made 

near  Lebanon  Mills '        172 

cited  on  Rhode  Island  coals 83, 84, 86 

Emmons,  E.,  cited  on  Cambrian  rocks 104, 109 

Erosion,  glacial,  amount  of 71-76 

relatively  rapid  and  etfective  work  of 73 

Ettoblattinaclarkii,  occurrence  of 203 

Ettoblattina  exilis,  occurrence  of 203 

Ettoblattina  gorhami,  occurrence  of 203 

Ettoblaiitina  illustris,  occurrence  of 203 

Ettoblattina  reliqua,  occurrence  of 203 

Ettoblattina  scholfieldi,  occurrence  of 203 

Ettoblattina  sp.,  occurrence  of 203 

F. 

Fall  River,  Mass.,  arkose  deposits  near 51-52 

granite  and  Carboniferous  rocks  at 270 

Faulting,  occurrence  and  directions  of 310, 377 

Felsites,  occurrence  of lie,  153-155 

Ferns,  fossil,  occurrence  of 347,  363,  374, 378 

Finlay,  J.  R.,  acknowledgments  to 211 

cited  on  boundary  of  Carboniferous  basin 127 

Finlay,  F.  H.,  and  Richmond,  H.  I.,  cited  on  gabbro 

hills  of  Sharon,  Mass H8 

Flint  Point,  R.  I.,  arkose  and  shaly  rocks  near 283 

Flora,  Carboniferous 170, 181, 204 

Foerste,  A.  F. ,  area  surveyed  by xvii 

cited  on  quartz  veins  in   granite-porphyry  at 

Diamond  Hill,  R.  I ns 

cited  on  Wamsutta  group 141 

cited  on  fence- wall  geology 102 

cited  on  horizon  of  limestone  at  Nahant 388 

description  of  Cambrian  deposits  of  the  south- 
western part  of  the  basin  prepared  by 381,  393 

description  of  the  Carboniferous  strata  of  the 
southwestern  portion  of  the  basin  prepared 

by 215-380 

"Wamsutta  group  of 141 

Foerste,  A.  F.  and  Shaler,  N.  S.,  cited 109 

Fogland  Point,  R.  I.,  conglomerate  at 278-279 

Folding,  age  of  the 22-23 

types  of 16-17,21-22 

Folding  and  faulting,  difficulties  of  stratigraphic  de- 
termination occasioned  by 101 

Folds,  forms  and  attitudes  of 16-17,  21-22 

plan  of 27 

Foolish  Hill,  Foxboro,  Mass.,  basal  arkose  at 135 

Carboniferous  strata  at 188 

exposure  of  red  rocks  of  Wamsutta  groups  at  . .  143, 144 

fault  at 128 

section  at 190 

Fordilla  troyensia,  occurrence  of 389 


398 


INDEX. 


Page. 

fort  Adams,  rocks  at - 317 

Fort  Greene  Park,  rocks  of 309 

Forty  Steps,  Newport,  E.  I.,  rocks  at  and  near.  3U-3U,  372 

Fosboro,  Mass.,  coal  bed  in 205 

gabbro  and  granitite  at 118 

Fox  Hill,  Conanicut  Island,  R.  I.,  geologic  features 

of 228-229 

Franklin  Society  of  Providence,  R.  I.,  list  of  Coal 

Measure  plants  compiled  by 205 

records  of  well  borings  preserved  by 163 

Fuller,  M.  L.,  cited  on  Carboniferous  area  nortk  of 

Brockton 129 

G-. 

Gabljro,  occurrence  of ,-  118 

Gardeners  Neck,  Mass.,  Carboniferous  beds  on 267-268 

Gay  Head,  Martbas  Vineyard,  deposits  of  arkose  at-  54 

Geological  succession  of  formations  in  tbe  Basin 8-10 

Gerablattina  fraterna.  occurrence  of 203 

Gerablattina  scapularis,  occurrence  of 203 

Glacial  erosion,  amount  of 71-76 

difficulties  of  strati  graphic  determination  occa- 
sioned by 102-103 

effects  and  products  of 64-77 

relatively  rapid  and  effective  work  of 73 

Goat  Island,  R.I. ,  rocks  of 3U9 

Goat  Rock  Cliff,  near  Plainville,  R.  I.,  section  at...  180-181 

Goniopteris  (Pecopteris)  unita,  occurrence  of 204 

Gooch,  F.  A.,  analysis  of  coal  by 83, 161 

Gould  Island,  R.i.,  rocks  of 272-273,356 

Granite,  areas  of 262-263 

Granite-porphyry,  areas  of 117 

Granitic  rocks,  occurrence  and  character  of 114^-116 

Granitites,  occurrence,  character,  and  age  of 114-116,118 

Griswold,  L.  S.,  and  Marbut,  C.  F.,  cited  on  bound- 
ary of  Carboniferous  Basin 127-128 

Gull  Rocks,  R.  I.,  shale  of 307 

H. 

Hall,  -James,  orogeuic  theory  of 16 

Halsey  Farm,   Silver  Spring,  R.  I.,  sections  at  and 

near 166, 167 

Hamilton,  R.  I.,  Carboniferous  rocks  near 249,  250' 

Hammond  Hill,  Mass.,  Kingstown  series  at 344 

Hanging  Rock  ridge,  features  and  structures  of 367, 368 

Hanging  Rocks,  conglomerates  of 298-300 

pre-Carboniferous  area  near 300-303 

Hanover,  Mass.,  Carboniferous  sandstone  rock  at . . .  193, 194 
Hanover  Four  Corners,  Mass..  Coal  Measure  beds. 

near 194 

Hardon  mine,  analyses  of  coal  from 190, 191 

High  Hill  Point,  R.  I.,,  conglomerate  at 278 

Hills  Grove  Station,  R.  I.,  Carboniferous  beds  near. .  257 

Hills  Grove,  R.  I.,  sandstone  at 334 

Hitchcock,  C.  H.,  cited  on  supposed  Devonian  rocks.  141 

cited  on  occurrence  of  coal  near  Cochesett  Sta- 
tion    192 

coal  near  Cochesett  Station  shown  on  map  of 192 

features  of  geologic  map  prepared  by 125, 133 

Hitchcock,  Edward,  analysis  of  limestone  by .---  150 

cited  on  age  of  the  granite  rocks 114 

-  cited  on  boundary  of  Carboniferous  basin 127 

cited  on  dip  of  beds  near  filansfield  Junction...-  190 

cited  on  flora  of  shales  at  Mansfield 191 


Hitchcock,  Edward,  cited  on  occurrence  of  coal  in 

Fosboro 190 

cited  on  Rosbury  (=Dighton)  conglomerate 184 

cited  on    supposed    Devonian    and  other   rock 

strata 141 

cited  on  the»coal  beds  of  tbe  basin 205-207 

cross  section  of  Carboniferous  area  of  Narragan- 

sett  Basin  cited  from 123 

early  attempts  to  discriminate  geologic  horizons 

by 133 

features  of  early  geologic  maps  prepared  by 124 

Hoppin    Hill,    North  Attleboro.    Mass.,   Cambrian 

rocks  and  fossils  at  and  near 386,388-392 

view  of 384 

Hope  Island,  R.  I.,  rocks  and  features  of 235-237. 341-342 

Hornblende  rock,  occurrence  and  cbaracter  of 117 

Hunt,  T.  Sterry,  geologic  correlation  of  limestone  of 

Carboniferous  basin  suggested  by 151 

Hunts  Mills,  R.  I.,  section  at 169 

Hyolithellus  micans,  occurrence  of 388, 389,  393 

Hyolithes  americanus,  occurrence  of 390 

Hyolithes  biUingsi,  occurrence  of 389 

Hyolithes  communis,  occurrence  of 388,  392 

Hyolithes  communis  var.  emmonsi,  occurrence  of. . .  390, 392 

Hyolithes  micans,  occurrence  of 386 

Hyolithes  princeps,  occurrence  of 386,  389,  393 

Hyolithes  quadricostatus,  occurrence  of 390 


I. 


Igneous  action,  relation  of  plastic  movement  of  rock 

to 19 

Igneous    intrusions,    difficulties     of     stratigraphic 

determination  occasioned  by 101 

Igneous  rocks,  occurrence  and  character  of. .  152-155, 114-118 

Insect  fauna  of  the  Rhode  Island    coal  field,  list 

comprising 202,  203 

Iron  Hill,  Cumberland,  E.  I.,  bowlder  train  at 72, 73, 76 

iron  ore  of 89 

Iron  ores,  occurrence  of 88-90 

Island  Rocks,  shales  and  slates  of 286 


J. 


Jackson  C.  T.,  cited  on  coal  beds  at  Portsmouth 

mine 207 

cited  on  coal  bed  in  Cranston 206 

cited  on  origin  of  Carboniferous  clay  slate 202 

cited  on  primary  rocks 104 

cited  on  strike  and  dip  of  strata  inclosing  coal 

beds 189,190 

cited  on  strike  and  dip  of  strata  inclosing  coal 

beds  near  Mansfield  Junction. . . : 189. 190 

features  of  early  geologic  map  prepared  by 124 

Jacobs  Point,  conglomerate  near 261 


K. 


Kingstown  sandstones,  divergent  views  of  authors 

as  to  value  of --.       xviii 

geologic  equivalents  of 134,358,359,361-363 

folding  in 345,346,394 

thickness  of 345,  346 

Kingstown  series,  geologic  place  and  equivalents  of.  134 

occurrence  and  character  of 159-104, 331-347 


INDEX. 


399 


Page. 
Kingstown  aeries,  Tiew  of  contact  of  pegmatite  with .  242 
view  showing  cross  stratification  in  pebbly  sand- 
stone of 248 

view  showing  sandstone  gneiss  of 334 

L. 

Landes,  Harry,  acknowledgments  to 211 

Lane,  A.  C,  Cambrian  fossils  discovered  by 388 

LawtonsValley,  E.  I.,  rocks  near 319,320,326,327 

Lebanon  Mills,  Mass.,  section  of  boring  near 170-172 

Tenmile  Kiver  beds  at 164 

Leonards  Corners,  K.  I.,  exposure  of  Tenmile  Eiver 

beds  in  quarry  near 165 

Lesqnereuj,  L.,  cited  on  rarity  of  occurrence  of 

SigiUaria  volzii 181 

fossil  plants  identified  by 191,204 

Level,  recent  changes  of 46-47 

Lily  Pond,  K.  I.,  granite  near 31G 

Lime  Kock,  K.  I.,  Carboniferous  shales  of 309 

limestone  beds  near 318 

Lime  Kock  quarries,  disconnected  dike  at 107, 108 

Limestone,  analysis  of 150 

Lingula  antiqua,  occurrence  of 109 

Lingula  prima,  occurrence  of 109 

Lithologic  characters,  rocks  of  different  ages  show- 
ing duplication  of 100 

i-ocks  of  similar  age  showing  local  variations  of.  100 

Little  Compton,  K.  I.,  Cambrian  rocks  in 383 

shales  and  slates  near 281,282 

Little  Lime  Eock,  E.  I.,  Carboniferous  shales  of 309 

Logan,  "W.E.,  features  of  geologic  map  prepared  by.  125 

Logan  and  Hall  cited 141 

Lyell,  Charles,  early  geologic  map  prepared  by 133 

features  of  geologic  map  prepared  by 125 

JSZ. 

McCormick's  quany,  near  Leonards  Corners,  E.  I., 

exposure  of  Tenmile  Eiver  beds  at 165 

McCurry's  Point,  E.I.,  rocks  near 290 

Maclure,  William,  delineation  of  boundaries  of  Car- 
boniferous basin  by 124 

Mansfield,  analyses  of  coal  from 191 

Carboniferous  beds  near 188-191 

coal  beds  at 79,80,205 

fiora  of  shales  at 191 

gabbro  and  granitite  at 118 

section  of  Coal  Measures  in 190 

section  of  rocbe  moutonn^e  near 188 

Mansfield  beds,  table  showing  geologic  place  and 

equivalents  of. 134 

Manton,  Cumberland  quartzite  at 106-107 

Map,  geological 210,  394 

Maps  and  sections  of  the  Carboniferous  basin  . .  121, 122, 123 

citations  of 124-125 

notes  on 594 

Marbut,  C.  F.,  and  Griswold,  L.  S.,  cited  on  bound- 
ary of  Carboniferous  basin 127-128 

Margins  of  basin,  greater  folding  at 16-18 

Marine  action  in  erosion  and  in  land  making,  char- 
acter and  extent  of 44-46,  76 

Marthas  Vineyard,  deposits  of  arkose  on 54 

geologic  history  of 24 

erogenic  action  in 24 

Pliocene  folding  on 13 

i  of  glacial  deposit  in ^ 71 


Merrill,  G.  P.,  cited  on  diorite  of  Paradise  Eocks 

Metamorphism,  dilficulties  of  strategraphic  determi- 
nation occasioned  by 

map  showing  areas  of '. 

Miantonomy  Hill,  E.  I.,  conglomerates  at  and  near. 

Microdiscus  bellimarginatus,  occurrence  of 

Microdiscus  lobatus,  occurrence  of 

Middleboro  quadrangle,  Carboniferous  beds  in 

Mill  Cove,  Boston  Basin,  Cambrian  rocka  and  fossils 


304, 305 
369-371 
390,  392 


of. 


Millers  Eiver,  Cumberland,  E.  I.,  conglomerate  beds 
at 

geologic  section  of  strata  near 

Millers  Eiver  conglomerates,  table  showing  geologic 

place  and  equivalents  of 

Moraines,  frontal,  characters  of 

Morton  Park,  E.  I.,  rocks  of ; 

Mountain  making,  features  of 

Mount  Desert  Basin,  geologic  history  of 

Mount  Hope,  K.  I.,  granite  at 

Mylacridse,  occurrence  of 

Mylacris  packardii,  occurrence  of 


jS". 

Kahant,  Cambrian  rOcka  and  fossils  at 388 

Nannaquacket  Pond,  granite  near 272 

Carboniferous  rocks  near 280-281 

arkose  and  conglomerates  near 378, 379 

(  Narragansett    Pier,    E.  I.,    Carboniferous  rocks  at 

and  near 245-246 

Natick,  equivalence  of  Tiverton  arkoses  to  those  at.  379 

rocks  at  and  near 253-256,  375-376,  383-385 

Neuropteris  angustifolia,  occurrence  of 191 

ISTeuropteris  decipiens,  occurrence  of 204 

Neuropteris  dentata,  occurrence  of 204 

iNeuropteris  heterophylla,  occurrence  of 191 

Neuropteroidea,  occurrence  of 202 

Kewberry,  J.  S.,cited  ou  cycles  of  deposition 49 

!N"ewport,  E.  I.,  Aquidneck  shales  near 356 

coal  beda  at 207 

coal  seams  and  coal  plants  in  excavations  at 372 

position  of  Carboniferous  conglomerate  at 373 

strata  beneath 313 

Newport  cliffs.  Carboniferous  rocka  of 310-314 

faulting  near 310 

fossil  ferns  found  at 374 

problematic  geologic  position  of  section  at 371-372 

Newport  Harbor,  rocks  of  islands  in 307-310 

Newport  Neck,  rocks  of 316-318,383 

Nonquit  Point,  Carboniferous  rocka  near 279 

Nonquit  Pond,  sandstone  and  coaly  shale  near 275-276 

Norfolk  County  basin,  occurrence  of  red    beds  of 

"Wamsutta  group  in 148-149 

North  Attleboro,  Mass.,  basal  arkose  at 135 

Cambrian  rocks  and  fossils  in  and  near 386-392 

exposure  of  rocks  of  "Wamsutta  group  near 145-146 

fossil  plants  found  near 337 

geologic  section  near 145 

sketch  map  of  Cambrian  localties  at 386 

view  of  faulted  diabase  dikes  in 152 

view  of  granite  mass  at 334 

view  of  outcrop  of  Wamsutta  group  in 146 

North  Foxboro,  Mass.,  gabbro  and  granitite  at 118 

Norton,  Mass'.,  section  in 195-196 


400 


IISTDEX. 


O.  Page. 

Obolella  atlautica,  occurrence  of 390 

Obolella  crassa,  occurrence  of 390, 392 

Obolns,  occurrence  of . . .  109, 110,  111,  112, 146,  314,  366,  382,  384 

Obolus  (Lingulella)  rogersi,  occurrence  of 113 

Obelus  (Lingulobulus)  affinis,  occurrence  of 113,  382 

Obolus  (Lingulobolus)  rogersi,  occurrence  of 382 

Obolus  (Lingulobulus)  epissus,  occurrence  of 113,382 

Ocbre  Point,  conglomerate  of 311-312 

Odontopteria,  occurrence  of 170,  203-204 

Oilontopteris  bairdii,  occurrence  of 204 

Odontopteria  cornuta,  occurrence  of 204 

Odontopteris  neuropteroides,  occurrence  of 204 

Odontopteris  obtusiloba,  occurrence  of 204 

Odontopteris  reicbiana,  occurrence  of 20i 

Odontopteris  reichiana  var.  latifolia,  occurrence  of-.  204 

Odoutopteris  stiebleriana,  occurrence  of 204 

Olenellus  -walcotti,  occurrence  of 390 

Olenellus  zone,  occurrence  and  character  of  rocks  of.     8, 105, 

38&-393 

OUgocarpia  gutbieri,  occurrence  of 204 

Organic  geology,  features  of 202-210 

Orogenic  action,  features  and  results  of 20-25,  32-36 

Orogenic  history,  features  of 7, 8, 9-10 

Orthopteroidea,  occurrence  of 202-203 

Overtlirust  phenomena,  character  of 25-27 

Pachet  Brook,  granite  near 275 

slates  and  shales  near 281 

Packard,  A.  S. ,  acknowledgments  to 211 

cited  on  fossils  of  Pawtucket  shales 202 

Palseoblattaripe,  occurrence  of 202 

Paradise  Eocks,  conglomerates  of 295-298 

Paralogus  asschnoides,  occurrence  of - .  203 

Parsons,  W.  E.,  acknowledgments  to 211 

Passamaquoddy  Basin,  geologic  history  of 13-15 

Pattaquamscott  River,  Carboniferous  rocks  near 246-247 

Pawtucket,  K.  I.,  coal  beds  at 79 

conglomerate  in 141 

Cranston,  beds  at  and  near 159-162 

exposure  of  red  rocks  of  "Wamsutta  group  at 148 

fossil  insects  from 202,  203,  204 

Pawtucket  shales,  exposures  of 162 

fossils  of 202 

table  showing  geologic  place  and  equivalents  of.  134 

Pawtuxet  Kiver,  Carboniferous  beds  near 259 

Pebbles,  conditions  of  making  of 56-58 

compressive  distortion  of 18 

Pecoi>teri8,  occurrence  of 168, 170, 191 

Pecopteris  abbreviata,  occurrence  of 204 

Pecopteris  arborescens,  occurrence  of 204 

Pecopteris  borealis,  occurrence  of 191 

Pecopteris  dentata,  occurrence  of 204 

Pecopteris  gigantea,  occurrence  of 191 

Pecopteris  hemiteloides,  occurrence  of 204 

Pecopteris  lepidorachis,  occurrence  of 204 

Pecopteris  loschii,  occurrence  of 191 

Pecopteris  miltoni,  occurrence  of 204 

Pecopteris  unita,  occurrence  of 170 

Pegmatite  dikes,  view  of 376 

Pegmatites,  views  of 244 

Pembroke,  Mass..  Carboniferous  and  other  rocks  near  194 

Perrins,  anticlinal  exposure  of  low  beds  at 169-170 

Perry,  J.  H.,  cited 126 


Pierces  Pasture,  near  Pondville  Station,  Mass.,  sec- 
tion at  135-13U 

Plainville,  Mass.,  section  in 183 

view  of  Carboniferous  sandstones  at 186 

Plainville  Valley,  "Wrenthara,  Mass.,  view  of 180 

Plants,  fossil,  occurrence  of 170, 

181,  204,  260,  261,  268,  275,  276,  285,  289,  293, 

314,  320,  321,  326,  347,  363,  372,  374,  378,  387 

Plastic  movement  of  rock,  regional  distribution  of . .       lS-19 

Platyceras  prima; vum,  occurrence  of 390 

Pleurotomaria   (Kaphistoma)  attleboroensis,   occur- 
rence of 389 

Plympton  felsites,  occurrence  and  character  of 116 

Pondville,  Mass.,  section  in 135-136 

Pondville  group,  features  of  beds  of »...  135-141 

table  showing  geologic  place  and  equivalents  of.         134 

Fontiac,  Carboniferous  rocks  near 256 

Popasquash  Neck,  Carboniferous  &andstone  on 261 

Portsmouth,  R.  I.,  analyses  of  coal  from 83 

Carboniferous  rocks  near 288-289 

conglomerate  in 373 

coal  beds  at 81, 321 

record  of  boring  in 321-325 

value  of  coal  from 83-85 

Portsmouth  coal  mine,  operations  at 206-207 

Portsmouth  Grove  Station,  rocks  near 328-329 

Potowomut  River,  Carboniferous  rocks  near 251-252 

Potsdam  sandstone,  pebbles  and  fossils  of 109-113 

Pre-Cambrian  rocks,  occurrence,  character,  and  re- 
lations of 104-109 

Pre-Carboniferous  rocks,  fossils  of 381, 382,  383, 384 

occurrence  and  character  of 104-113,  381-385 

Prices  Neck,  rocks  near 316 

Protophasmida,  occurrence  of 203 

Providence,  R.  I.,  coal  bed  at 206 

Cranston  beds  at  and  near 159-164 

hypothetical  geologic  section  through 160 

record  of  well  sunk  at 161 

view  of  glaciated  Carboniferous  ridge  at 162 

view  of  pre-Carboniferous  rocka  near 126 

Providence  River,  Carboniferous  beds  near 259-260 

synclinal  fold  in  Kingstown  series  near 345 

Prudence  Island,  R.  I.,  rocks  and  geologic  features 

of 237-241,342-343,345,350-351 

Prudence  Island,  Kingstown  series  on 342-343 

views  on 350.  352,  362 

Pseudopecopteris  dimorpha,  occurrence  of 204 

Pseudopecopteris  irregularis,  occurrence  of 191 

Pty choparia  attleboroensis,  occurrence  of 390 

Purgatory  chasm,  typical  conglomerate  at 365-366 

Purgatory  conglomerate,  occurrence  and  characterof  364—374 

table  showing  geologic  place  and  equivalents  of.  134 

Putnam,  B.  T.,  analyses  by 83 


Q. 


356 


Quaker  Hill,  Aquidneck  shales  near 

Quartz,  occurrence  of 155 

Quartzites,  occurrence  of 382, 383-384 

Quartz-porphyries,  occurrence  of 153, 155 

Raindrop  imprints,  view  of 178 

Rainfall  and  arkose,  relations  of 55-57 

Raynham,  coal  bed  in  .; ' 205 


INDEX. 


401 


Page. 

Ked  beds  of  "Wamsutta  group,  exposures  of. 142-149 

map  showing  areas  of 142 

Eed  color  of  Cambrian  and  Carboniferous  rocks,  ori- 

rrin  of 62-63, 115 

Eeaervoir  Pond,  Attleboro,  Mass.,  section  near 153 

Ehacopbyllum  adnascens,  occurrence  of 191 

Kbapbidiopsis  diveraipenna,  occurrence  of 202 

Kbode  Island  Coal  Measures,  table  sbowing  geologic 

place  and  eciuivalents  of 134 

Picbmond  Basin,  Virginia,  geologic  history  of 13-15 

Eidgway,  Thos.  S.,  cited  on  operations  of  the  Mans- 
field Coal  and  Mining  Company 205 

section  of  boring  near  Lebanon  Mills  made  by  ..  170-172 

Elpple-marked  sandstones,  view  of 178 

Biverside,  K.  I.,  geological  section  at  and  near 166 

synclinal  fold  in  Kingstown  Series  near 345 

Tenmile  Eiver  beds  near 166 

Eobinson  Hill,  North  Attleboro,  Mass.,  geologic  sec- 
tion at - 145 

Eocky  Hill,  Providence,  E.  T.,  view  of 162 

Eocky  Point,  E.  I.,  geologic  horizon  of  conglomer- 
ates of 346 

Eocky  Woods  conglomerate,  table  showing  geologic 

place  and  equivalents  of 134 

Eoger  "Williams  coal  mine,  Cumberland,  E.  I.,  opera- 
tions at 206 

Eogers,  'W.  B  ,  cited  on  Potsdam  sandstone 109 

Eoselsland,  E.I.,  rocksof 308,380 

Eoxbury  (—  Digbton)  conglomerate,  occurrence  of..  184-187 

Eumstick  Neck,  E.  I.,  Carboniferous  rocks  on 260,344 

synclinal  fold  near 345 

Eussell,  I.  C.,  cited  on  coloration  of  rocks 115 

S. 

Sachems  Eock,  East  Bridgewater,  Mass.,  Coal  Meas- 
ure beds  at 193 

Sachuest  Neck,  E.  I.,  arkose  and  pre- Carboniferous 

rocks  on 284-288,379 

Sakonnet  Eiver,  conglomerates  near 278-281 

Sakonnet  Eiver  syncline,  features  of 369 

Sakonnet  sandstones,  occurrence  and  thickness  of  . .         358, 

359-360 

Salterella  curvata,  occurrence  of 386,  389 

Sand  Point,  Prudence  Island,  E.  I.,  micaceous  shales 

at - 239-240 

Sandy  Point,  Aquidiieck  Island,  E.  I.,  Carboniferous 

shales  near 289-290 

Sapowet  Point,  E.  I.,  Carboniferous  rocks  near 280 

Saunderstown,  E.  1.,  Carboniferous  rocks  near 242,  248 

Kingstown  series  at 334 

Scerella  reticulata,  occurrence  of 390,  392 

Scbizopteris  (Ehacopbyllum)  trichomanoides,  occur- 
rence of 204 

Schrader,  F.  C,  observations  made  by 106, 107 

section  of  Goat  Eock  Cliff,  near  Plainville,  meas- 
ured by 180-181 

Scolithus,  occurrence  of  burrows  of 197 

Scholithus  linearis,  occurrence  of 109, 110,112 

Scudder,  S.H.,  cited  on  insect  fauna  of  tbe  Ehode 

Island  coal  field 202 

Sears,  John,  Cambrian  rocks  and  fossils  discovered 

by 388 

Sections,  geological 394 

Sections  and  maps,  notes  on 394 

Sedimentary  deposits,  thickness  of 31 

MON  XXXIII 26 


Sedimentation,  cycles  of 49-50 

Seekonk,  Mass.,  boring  showing  coal  at 86 

coal  bed  at 206 

exposures  and  sections  of  Carboniferous  rocks  in .  169-173 

Seekonk  beds,  occurrence  and  character  of 173-175 

Seekonk  Coal  Mining  Company,  section  of  boring 

made  for 170-172 

Seekonk  conglomerate,  occurrence  and  character  of .  174-175 
table  showing  geologic  place  and  equivalents  of.  134 

Seekonk  sandstones,  table  showing  geologic  place 

and  equivalents  of 134 

Sewammock  Neck,  Mass.,  sandstone  at 268 

Shaler,  N.  S.,  Cambrian  rocks  discovered  by 386 

cited  on  increased  erosion  due  to  narrowing  of 

glacier 74 

cited  on  Iron  Hill  bowlder  train 72 

cited  on  pre-Cambrian  rocks 104 

letter  of  transmittal  by sv 

preface  by xvii-xx 

report  on  general  geology  by 1-214 

Shaler,  N.  S.,  and  Foerste,  A.  P.,  cited  on  Cambrian 

fossils  from  North  Attleboro 109,141,386 

Sharon,  gabbro  hills  of 118 

Sharpies,  P.  P.,  photographs  made  by 211 

Shearing  planes,  areas  showing 20-21 

Sheep  Point,  rocks  of 314^315 

Sheldon  ville,  fault  at 127 

Shumatuscacant  Eiver,  fault  near 129 

Sigillaria  ?  occurrence  of 165, 191 

Sigillaria  volzii,  occurrence  of 181 

Silurian  rocks,  occurrence  of  pebbles  from 109-113 

Silver  Spring,  E.  I.,  fossil  insects  from 203 

view  of  Carboniferous  sandstones  at 166 

Silver  Spring  Station,  E.  I.,  sections  at  and  near  . . .  166, 167 

Sin  and  Plesb  Brook,  micaceous  schist  on 272 

Slate  Hill,  E.  I.,  rocks  at  and  near 320,329-330,356,364 

Smitbfield  limestones,  occurrence  and  character  of. .  107-109 

Smiths  Beach,  E.I.,  rocks  near 292 

Sueech  Pond,  E.  I.,  copper  and  iron  ores  near 109 

Cumberland  quartzite  at 106 

Sockanosset  Hill,  E.  I.,  Carboniferous  beds  at  and 

near 25fr-257 

Sockanosset  sandstones,  exposures  of 163 

table  sbowing  geologic  place  and  equivalents  of.  134 

Soils,  character  of 77-79 

South  Attleboro,  limestone  bed  at 149-151 

quartzose  conglomerate  near 140 

section  of  "Wamsutta  formation  at 149 

Spbenophyllum  dentatum ,  occurrence  of 191 

Sphenophyllum  equisetiformis,  occurrence  of 320 

Spbenophyllum  erasum,  occurrence  of 191 

Sphenopbyllum  oblongifolium,  occurrence  of 204 

Sphenophyllum  achlotbeimii,  occurrence  of 168 

Sphenophyllum  truncatum,  occurrence  of 191 

Sphenopteris  (Hymenophyllit«s)  furcata,  occurrence 

of 204 

Sphenopteris  lanceolata,  occurreuce  of 204 

Sphenopteris  salisburyi,  occurrence  of 191 

Spider,  Carboniferous,  occurrence  of 202 

Spindle  Eock,  Carboniferous  shales  of 309 

Steep  Brook,  Mass.,  arkose  deposits  at 51-52 

conglomerates  near 378 

granite  and  Carboniferous  rocks  at 269-270 

Stenotheca  curvirostra,  occiurence  of 390 

Stenotheca  rugosa,  occurrence  of 386, 388 

Stenotheca  rugosa  var.  abrupta,  occurrence  of 390,  392 


402 


INDEX. 


Stenotlieca  rugosa  var.  pauper,  occurrence  of 389 

Stratigrapbic  succession,  difficulties  of  determiniug.     99-103 

Stress,  diagram  showing  conditions  of 19 

rock  compression  and  elongation  by 17-lB 

Surf  and  current  action,  cliaracter  and  extent  of 

erosion  by 76 

Swansea,  conglomerates  and  shales  near 264-266, 373 

Swamp  areas,  agricultural  utilization  of 78-79 

Swan  Point  Cemetery,  sandstone  outcrox>  at "  163-164 

T. 

Taggarts  Ferry,  Purgatory  conglomerate  at 364 

Taunton,  coal  bed  in 205 

Coal  Measures  north  and  east  of 187-201 

record  of  artesian-well  boring  at 198-199 

section  near 199 

Taunton  quadrangle,  Carboniferous  beds  in 195-200 

Taunton  Kiver,  features  of  course  of 200 

Tenmile  Eiver  beds,  exposures,  sections,  and  fossils 

of 164-173 

plant  remains  in 164, 168, 170 

table  showing  geologic  place  and  equivalents  of.  134 

Teschemacher,  J.  E.,  x>lant  remains  from  shales  at 

ilansfield  described  by 191 

Till,  thickness  and  character  of 69-70 

Tiverton,  K.  I.,  arkose  in, 378 

equivalence  of  ^Natick  arkoses  to  those  at 379 

granite  and  Carboniferous  rocks  at 271-272 

Tiverton  Pour  Corners,  K.  I.,  Carboniferous  beds 

near 280-281 

granite  at 274 

Topsfield,.  Mass.,  Cambrian  rocks  at 388 

Tower,  G- W.,  acknowledgments  to 211 

Tower  Hill,  K.  I.,  Carboniferous  and  intrusive  rocks 

at 246-247 

Town  Pond,  P.  I.,  rocks  near 321 

Townsend  Hill,  Mass.,  granite  and  arkose  at 270 

Triassic  rocks,  eastern  United  States 11-12 

Valley  Palls.  E.I.,  coal  beds  at 80,206 

fossil  insects  from 204 

Yalley  Falls  coalmine,  operations  at 206 

YanHise,  C.  P.,  cited 125 

Volcanoes,  Carboniferous,  geologic  evidence  indicat- 
ing   155-166 

Wadsworth,  M.  E.,  cited  on  age  of  granitic  rocks 114 

cited  on  iron,  ore  of  Cumberland,  P.  1 89 

"Walcott,  C.  D.,  cited  on  age  of  chert  pebbles  from 

Marthas  Vineyard 113 


Page. 
TValcott,  C.  D.,  cited  on  brachiopod  fauna  of  quartz- 
itic    pebbles  from  Carboniferous    conglom- 
erate    366,  382 

cited  on  Cambrian  fossils Ill,  113, 146. 366, 382 

cited  on  intraformational  conglomerates 189 

cited  on  Upper  Cambrian  rocks 109 

geologic  horizon  determined  by 386 

AVamsutta  group,  dikes  in  beds  of 1 52 

features  of  rocks  of 141-158 

flora  of 158 

folding  of 15G-158 

igneous  associates  of 152-155 

section  of 149 

table  showing  geologic  place  and  equivalents  of.         134 

view  of  outcrop  of 146 

volcanic  rocks  in 155-156 

"Wainwright,  Eobert,  acknowledgments  to 211 

■\ralkers  Cove,  granite  at 263 

"Warren,  P.  I.,  conglomerates  and  shales  near 266-267 

AYarren  Neck,  P.  I.,  Carboniferous  beds  on 264,373 

Warwick,  P.  I.,  Kingstown  series  in 335,336,342 

Warwick  Keck.  P.  I.,  Carboniferous  beds  on.. .  258,  336-337 
Watchemocket  Cove,  P.  I.,  Tenmile  River  beds  near.  166 

Watsons  Pier,  P.  I.,  Carboniferous  rocks  near 243-244 

view  of  coarse  pegmatites  at 244 

view  of  contact  of  i>egmatites  and  shales  at 242 

Wesquage  Pond,  P.  I.,  rocks  near 243,  333 

West  Mansfield,  Mass.,  view  of  rocks  at 188 

West  Newbury,  Mass.,  Cambrian  rocks  in 3S8 

Westville,  Mass..  section  in 199 

Westville  shales,  table  showing  geologic  place  and 

equivalents  of 134 

Whiteville,  red  rocks  of  Wamsutta  group  at 144 

Wickford,  Carboniferous  rocks  near 251 

Wiokford  Junction,  Kingstown  series  at 344 

Willis,  Bailey,  cited 168 

Windmill  Hill,  P.  I.,  conglomerates  at  and  near 277 

Winneconnet,  Mass.,  Carboniferous  beds  near 196  197 

map  showing  area  of  metamorphism  near 120 

Wolff,  J.  E  ,  acknowledgments  to 211 

Woods  Castle,  Carboniferous  rocks  near 293 

fossil  ferns  found  at 293,  374 

Woodworth,  J.B.,  area  examined  by xvii 

bibliography  of  Cambrian    and    Carboniferous 

rocks  prepared  by 212-214 

cited 141,167 

description  of  the  northern  and  eastern  portion 

of  the  basin  prepared  by 91-210 

fossil  plants  discovered  by 387 

paper  on  northern  and  eastern  portions  of  the 

basin  by 91-214 

Wrentbam,Mass.,  coal  bed  in 182,205 

exposures  of  Attleboro  sandstone  at 144-145 

view  near 180 


[Monograph  XXXIII.] 


The  statute  approved  March  3,  1879,  establishing  the  United  States  Geological  Survey,  contains 
the  following  provisions : 

"The  publications  of  the  Geological  Survey  shall  consist  of  the  annual  report  of  operations,  geo- 
logical and  economic  maps  illustrating  the  resources  and  classification  of  the  lands,  and  reports  upon 
general  and  economic  geology  and  paleontology.  The  annual  report  of  operations  of  the  Geological 
Survey  shall  accompany  the  annual  report  of  the  Secretary  of  the  Interior.  All  special  memoirs  and 
reports  of  said  Survey  shall  be  issued  in  uniform  quarto  series  if  deemed  necessary  by  the  Director,  but 
otherwise  in  ordinary  octavos.  Three  thousand  copies  of  each  shall  be  published  for  scientific  exchanges 
and  for  sale  at  the  price  of  publication ;  and  all  literary  aud  cartographic  materials  received  in  exchange 
shall  be  the  property  of  the  United  States  and  form  a  part  of  the  library  of  the  organization :  And  the 
money  resulting  from  the  sale  of  such  liublioations  shall  be  covered  into  the  Treasury  of  the  United 
States." 

Except  in  those  cases  in  which  au  extra  number  of  any  special  memoir  or  report  has  been  sup- 
plied to  the  Survey  by  special  resolution  of  Congress  or  has  been  ordered  by  the  Secretary  of  the 
Interior,  this  oliBce  has  no  copies  for  gratuitous  distribution. 

ANNUAL  EEPOETS. 

I.  First  Annual  Keport  of  the  United  States  Geological  Survey,  by  Clarence  King.  1880.  8°.  79 
pp.     1  map. — A  preliminary  report  describing  plan  of  organization  aud  publications. 

II.  Second  Annual  Keport  of  the  United  States  Geological  Survey,  1880-'81,  by  J.  W.  Powell 

1882.  8-^.     Iv,  588  pp.     62  pi.     1  map. 

III.  Third  Annual  Eeport  of  the  United  States  Geological  Survey;  1881-'82,  by  J.  W.  Powell. 

1883.  8".     xviii,  56-1  iip.     67  pi.  and  maps. 

IV.  Fourth  Annual  Report  of  the  United  States  Geological  Survey,  1882-'83,  by  J.  W.  Powell. 

1884.  8"^.     xxxii,  473  pp.     83  pi.  and  maps. 

V.  Fifth  Annual  Eeport  of  the  United   States   Geological   Survey,  1883-'84,  by  J.  W.  Powell. 

1885.  8°.     xxxvi,  469  pp.     58  pi.  and  maps. 

VI.  Sixth  Annual  Eeport  of  the  United  States  Geological  Survey,  1884-'85,  by  J.  W.  Powell. 
1885.     8°.    xxix,  570  pp.     65  pi.  and  maps. 

VII.  Seventh  Annual  Eeport  of  the  United  States  Geological  Survey,  1885-'86,  l)y  J.  W.  Powell. 

1888.  8°.     XX,  656  pp.     71  pi.  aud  maps. 

VIII.  Eighth  Annual  Eeport  of  the  United  States  Geological  Survey,  1886-'87,.by  J.  W.  Powell. 

1889.  8°.     2  pt.     xix,  474,  xii  pp.,  53  pi.  and  maps;  1  pre]. .leaf,  475-1063  pp.,  54-76  pi.  and  maps. 

IX.  Ninth  Annual  Report  of  the  United  States  Geological  Survev,  1887-'88,  by  J.  W.  Powell. 

1889.  8".     xiii,  717  pp.     88  pi.  and  maps. 

X.  Tenth  Annual  Eeport  of  the  United  States  Geological   Survey,  1888-'89,  by  J.  W.  Powell. 

1890.  8°.     2  pt.     XV,  774  pp.,  98  pi.  aud  maps ;  viii,  123  pp. 

XI.  Eleventh  Annual  Report  of  the  United  States  Geological  Survey,  1889-90,  by  J.  W.  Powell. 

1891.  8"^.     2  pt.     XV,  757  pp.,  66  pi.  and  maps ;  ix,  351  pp.,  30  pi.  and  maps. 

XII.  Twelfth  Annual  Eeport  of  the  United  States  Geological  Survey,  1890-'91,  by  J.  W.  Powell. 
1891.     8°.    2  pt.,  xiii,  675  pp.,  53  pi.  and  maps ;  xviii,  .576  pi3.,  146  j)l.  and  maps. 

XIII.  Thirteenth  Annual  Report  of  the  United  States  Geological  Survey,  1891-'92,  by  J.  W. 
Powell.  1893.  8"^.  3  pt.  vii,  240  pp.,  2  maps;  x,  372  pp.,  105  pi.  and  maps;  x'i,  486  pp.,  77  pi.  and 
maps. 

XIV.  Fourteenth  Annual  Report  of  the  United  States  Geological  Survey,  1892-'93,  by  J.  W. 
Powell.    1893.     8'^.     2  pt.     vi,  321  pp.,  1  pi. ;  xx,  597  pp.,  74  pi.  and  maps. 

XV.  Fifteenth  Annual  Eeport  of  the  United  States  Geological  Survey,  1893-'94,  by  J.  W.  Powell. 
1895.     8'-\     xiv,  755  pp.,  48  pi.  and  maps. 

XVI.  Sixteenth  Annual  Eeport  of  the  United  States  Geological  Survey,  1894-95,  Charles  D. 
Walcott,  Director.  1895.  (Part  I,  1896.)  8"^.  4  pt.  xxii,  910  pp.,  117  pi.  and  maps;  xix,  598  pp.,  43 
pi.  and  maps;  xv,  646  pp.,  23  lA. ;  xix,  735  pp.,  6  pi. 

XVII.  Seventeenth  Annual  Eeport  of  the  United  States  Geological  Survey,  1895-96,  Charles 
D.  Walcott,  Director.  1896.  8".  3  pt.  in  4  vol.  xxii,  1076  pp.,  67  pi.  and  maps;  xxv,  864  pp.,  113  pi. 
and  maps;  xxiii,  542  pp.,  8  pi.  and  maps;  iii,  543-1058  pp.,  9-13  pi. 

XVIII.  Eighteenth  Annual  Report  of  the  United  States  Geological  Survey,  1896-'97,  Charles  D. 
Walcott,  Director.     1897.    (Parts  II  and  III,  1898.)     8^.    5  pt.  in  6  vol.     1-440  pp.,  4  pi.  and  maps;  i-v, 


II  ADVERTISEMENT. 

1-653  pp.,  105  pi.  and  maps;  i-v,  1-861  pp.,  118  pi.  and  maps:  i-x,  1-756  pp.,  102  pi.  and  maps;  i-xii, 
1-642  pp.,  1  pi. ;  643-UOO  pp. 

XIX.  Nineteenth  Annual  Report  of  the  United  States  Geological  Survey,  1897-'98,  Charles  D. 
AValoott,  Director.     1898.     8".     6  pt.  in  7  vol. 

MONOGRAPHS. 

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II.  Tertiary  History  ofthe  Grand  Canon  District,  with  Atlas,  by  Clarence  E.  Dutton,  Capt.,  U.  S.  A. 
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III.  Geology  of  the  Comstock  Lode  and  the  Washoe  District,  with  Atlas,  by  George  F.  Becker. 
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IV.  Comstock  Mining  and  Miners,  by  EliOt  Lord.     1883.     4^.     xiv,  451  pp.     3  pi.     Price  $1.50. 

V.  The  Copper-Bearing  Rocks  of  Lake  Superior,  by  Roland  Duer  Irving.  1883.  i^.  xvi,  464 
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VI.  Contributions  to  the  Knowledge  of  the  Older  Mesozoic  Flora  of  Virginia,  by  William  Morris 
Fontaine.     1883.     4°.     xi,  144  pp.     54 1.     54  pi.     Price  $1.05. 

VII.  Silver-Lead  Deposits  of  Eureka,  l^evada,  by  Joseph  Storv  Curtis.  1884.  4°.  xiii,  200  pp. 
16  pi.     Price  $1.20. 

VIII.  Paleontology  of  the  Eureka  District,  by  Charles  Doolittle  Walcott.  1884.  4-.  xiii,  298 
pp.     24 1.     24  pi.     Price  $1.10. 

IX.  Brachiopoda  and  Lamellibranchiata  of  the  Raritan  Clays  and  Greensand  Marls  of  New 
Jersey,  by  Robert  P.  Whitfield.     1885.     4".     xx,  338  pp.     35  pi.     1  map.     Price  $1.15. 

X.  Dinocerata.  A  Monograph  of  an  Extinct  Order  of  Gigantic  Mammals,  by  Othniel  Charles 
Mnxsh.     1886.     4°.     xviii,  243  pp.     56  1.     56  pi.     Price  $2.70. 

XI.  Geological  History  of  Lake  Lahontan,  a  Quaternary  Lake  of  Northwestern  Nevada,  by 
Israel  Cook  Russell.     1885.     4'^.     xiv,  288  pj).     46  jil.  and  maps.     Price  $1.75. 

XII.  Geology  and  Mining  Industry  of  Leadville,  Colorado,  with  Atlas,  by  Samuel  Franklin 
Emmons.     1886.     4".     xxix,  770  pp.     45  pi.  aud  atlas  of  35  sheets  foUo.     Price  $8.40. 

XIII.  Geology  ofthe  Quicksilver  Deposits  ofthe  Pacific  Slope,  with  Atlas,  by  George  F.. Becker. 
1888.     4^.     xix,  486  pp.     7  pi.  and  atlas  of  14  sheets  folio.     Price  $2.00. 

XIV.  Fossil  Fishes  and  Fossil  Plants  of  the  Triassic  Rocks  of  New  Jersey  and  the  Connecticut 
Valley,  by  John  S.  Newberry.     1888.     4°.     xiv,  152  jip.     26  pi.     Price  $1.00. 

XV.  The  Potomac  or  Younger  Mesozoic  Flora,  by  William  Morris  Fontaine.  1889.  4'^,  xiv, 
377  pp.     180  pi.     Text  and  plates  bound  separately.     Price  $2.50. 

XVI.  The  Paleozoic  Fishes  of  North  America,  by  John  Strong  Newberry.  1889.  4-.  340  pp. 
53  pi.     Price  $1.00. 

XVII.  The  Flora  of  the  Dakota  Group,  a  Posthumous  Work,  by  Leo  Lesquereux.  Edited  by 
F.  H.  Kuowlton.     1891.     4".     400  pp.     66  pi.     Price  $1.10. 

XVIII.  Gasteropoda  and  Cephalopoda  ofthe  Raritan  Clays  aud  Greensand  Marls  of  New  Jersev, 
by  Robert  P.  Whitfield.     1891.     4^.     402  jip.     50  pi.     Price  $1.00. 

XIX.  The  Peuokee  Iron-Bearing  Series  of  Northern  Wisconsin  aud  Michigan,  by  Roland  D. 
Irving  and  C.  R.  Van  Hise.     1892.     4°.     xix,  534  pp.     Price  $1.70. 

XX.  Geology  of  the  Eureka  District,  Nevada,  with  an  Atlas,  by  Arnold  Hague.  1892.  4".  xvii, 
419  pp.     8  pi.     Price  $5.25. 

XXI.  The  TertiarvRhyuchophorous  Coleoptera  ofthe  United  States,  by  Samuel  Hubbard  Scud- 
der.     1893.     i°.     xi,  206  pp.     12  pi.     Price  90  cents. 

XXII.  A  Manual  of  Topographic  Methods,  by  Henry  Gannett,  Chief  Topographer.  1893.  4°. 
xiv,  300  pp.     18  pi.    Price  $1.00. 

XXIII.  Geology  ofthe  Green  Mountains  in  Massachusetts,  by  Raphael  PumiJelly,  T.  Nelson  Dale, 
aud  J.  E.  Wolff.     1894.     i°.     xiv,  206  pp.     23  j>l.     Price  $1.30. 

XXIV.  Mollusca  aud  Crustacea  of  the  Miocene  Formations  of  New  Jersey,  by  Robert  Parr  Whit- 
field.    1894.    4°.     193  pp.     24  pi.     Price  90  cents. 

XXV.  TheGlacialLakeAgassiz,  by  Warren  Upham.   1895.   4°.  xxiv,658pp.   38  pL   Price  $1.70. 

XXVI.  Flora  of  the  Amboy  Clays,  by  John  Strong  Newberry;  a  Posthumous  Work,  edited  by 
Arthur  Hollick.     1895.     4°.     260  pp.     58  pi.     Price  $1.00. 

XXVII.  Geology  of  the  Denver  Basin  in  Colorado,  by  Samuel  Frauklin  Emmons,  Whitman  Cross, 
and  George  HomansEldridge.     1896.     4°.     556  pp.     31  pi.     Price  $1.50. 

XXVIII.  The  Marquette  Iron-Bearing  District  of  Michigan,  with  Atlas,  by  C.  R.  Van  Hise  and 
W.  S.  Bayley,  includiug  a  Chapter  on  the  Republic  Trough,  by  H.  L.Smyth.  1895.  4°.  608  pp.  35 
pi.  aud  atlas  of  39  sheets  folio.     Price  $5.75. 

XXIX.  Geology  of  Old  Hampshire  County,  Massachusetts,  ccTiprising  Frauklin,  Hampshire,  and 
Hampden  Counties,  by  Benjauiiu  Kendall  Emerson.     1898.     4°.     xxi,  790  pp.     35  pi.     Price  $1.90. 

XXX.  Fossil  Medusae,  by  Charles  Doolittle  Walcott.     1898.     4^.     ix,  201  pp.     47  pi.     Price  $1.50. 

XXXI.  Geology  of  the  Aspen  Mining  District,  Colorado,  with  Atlas,  by  Josiah  Edward  Spurr. 
1898.     4°.     XXXV,  260  pp.     43  pi.  aud  atlas  of  30  sheets  folio.     Price  $3.60. 

XXXII.  Geology  of  the  Yellowstone  National  Park,  Part  II,  Descriptive  Geology,  Petrography, 
and  Paleoutology.  by  Arnold  Hague,  J.  P.  Iddiugs,  W.  Harvey  Weed,  Charles  D.  Walcott,  G.  H.  Girty, 
T.  W.  Stanton,  and  F.  H.  Knowlton.     1899.     4°.     xvii,  893  pp.     121  pi.     Price- . 

XXXIII.  Geology  of  the  Narragansett  Basin,  by  N.  S.  Shaler,  J,  B.  Wood  worth,  and  August  F. 
Foerste.     1899.     4°.     xx,  402  pp.     31  pi.     Price .  ' 


ADVERTISEMENT.  Ill 

XXXV.  The  Later  Extinct  Floras  of  North  America,  by  John  Strong  Newberry;  edited  by 
Arthur  Hollick.     1898.     4°.     xviii,  295  pp.     68  pi.     Price  $1.25. 

Jv  preparation: 

XXXIV.  The  Glacial  Gravels  of  Maine  and  their  Associated  Deposits,  by  George  H.  Stone. 

XXXVI.  The  Crystal  Falls  Iron-Bearing  District  of  Michigan,  by  J.  Morgan  Clements  and 
Henry  Lloyd  Smyth;  with  a  Chapter  on  the  Sturgeon  River  Tongue,  by  William  Shirley  Bayley. 

XXXVII.  ilora  of  the  Lower  Coal  Measures  of  Missouri,  by  David  White. 

XXXVIII.  The  Illinois  Glacial  Lobe,  by  Frank  Leveiett. 

— Flora  of  the  Laramie  and  Allied  Formations,  by  Frank  Hall  Knowltou. 

BULLETINS. 

1.  On  Hypersthene-Andesite  and  on  Triclinic  Pyroxene  in  Augitic  Rocks,  by  Whitman  Cross, 
with  a  Geological  Sketch  of  Buffalo  Peaks,  Colorado,  by  S.  F.  Emmons.  1883.  8°.  42  pp.  2  pi, 
Price  10  cents. 

2.  Gold  and  Silver  Conversion  Tables,  giving  the  Coining  Values  of  Troy  Ounces  of  Fine  Metal, 
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3.  On  the  Fossil  Faunas  of  the  Upper  Devonian,  along  the  Meridian  of  76°  30',  from  Tompkins 
County,  N.  Y.,  to  Bradford  County,  Pa.,  by  Henry  S.  AVilliams.     1884.     8'"-.     36  pp.     Price  5  cents. 

4.  On  Mesozoic  Fossils,  by  Charles  A.  White.     1884.     8'^.     36  pp.     9  pi.     Price  5  cents. 

5.  A  Dictionary  of  Altitudes  in  the  United  States,  compiled  by  Henry  Gannett.  1884.  8°.  325 
pp.     Price  20  cents. 

6.  Elevations  in  the  Dominion  of  Canada,  by  J.  W.  Spencer.     1884.     8°.     43  pp.     Price  5  cents. 

7.  Mapoteca  Geologica  Americana.  A  Catalogue  of  Geological  Maps  of  America  (North  and 
South),  1752-1881,  in  Geographic  and  Chronologic  Order,  by  Jules  Marcou  and  John  Belknap  Maroon. 

1884.  8°.     184  pp.     Price  10  cents. 

8.  On  Secondary  Enlargements  of  Mineral  Fragments  in  Certain  Rocks,  by  R.  D.  Irving  and 
C.  R.  Van  Hise.     1884.     8°.     56  pp.      6  pi.     Price  10  cents. 

9.  A  Report  of  Work  done  in  the  Washington  Laboratory  during  the.  Fiscal  Year  1883-84.  F.  W. 
Clarke,  Chief  Chemist;  T.  M.  Chatard,  Assistant  Chemist.     1884.     8°.     40  pp.     Price  5  cents. 

10.  On  the  Cambrian  Faunas  of  North  America.  Preliminary  Studies,  by  Charles  Doolittle 
Walcott.     1884.     8°.     74  pp.     10  pi.     Price  5  cents. 

11.  On  the  Quaternary  and  Recent  MoUusca  of  the  Great  Basin;  -with  Description  of  New 
Forms,  by  R.  Ellsworth  Call.  Introduced  by  a  Sketch  of  the  Quaternary  Lakes  of  the  Great  Basin, 
by  G.  K.  Gilbert.     1884.     8°.     66  pp.     6  pi.     Price  5  cents. 

12.  A  Crystallographic  Study  of  the  Thinolite  of  Lake  Lahontan,  by  Edward  S.  Dana.  1884.  8°. 
34  pp.     3  pi.     Price  5  cents. 

13.  Boundaries  of  the  United  States  and  of  the  Several  States  and  Territories,  with  a  Historical 
Sketch  of  the  Territorial  Changes,  by  Henry  Gannett.     1885.     8°.     135  pp.     Price  10  cents. 

14.  The  Electrical  and  Magnetic  Properties  of  the  Iron-Carburets,  by  Carl  Barns  and  Vincent 
Strouhal.     1885.     8*^.     238  pp.     Price  15  cents. 

15.  On  the  Mesozoic  and  Cenozoie  Paleontology  of  California,  by  Charles  A.  White.  1885.  8°. 
33  px).     Price  5  cents. 

16.  On  the  Higher  Devonian  Faunas  of  Ontario  County,  New  Y'ork,  by  John  M.Clarke.  1885.  8°. 
86  pp.     3  pi.     Price  5  cents. 

17.  On  the  Development  of  Crystallization  in  the  Igneous  Rocks  of  Washoe,  Nevada,  with  Notes 
on  the  Geology  of  the  District,  by  Arnold  Hague  and  Joseph  P.  Iddings.  1885.  8°.  44  pp.  Price  5 
cents. 

18.  On  Marine  Eocene,  Fresh-Water  Miocene,  and  other  Fossil  Mollusca  of  Western  North 
America,  by  Charles  A.  White.     1885.    8^.     26  pp.     3  pi.     Price  5  cents. 

19.  Notes  on  the  Stratigraphy  of  California,  by  George  F.  Becker.   1885.   8°.   28  pp.   Price  5  cents. 

20.  Contributions  to  the  Mineralogv  of  the  Rocky  Mountains,  by  Whitman  Cross  and  W.  F.  Hille- 
braud.     1885.     8°.     114  pp.     1  pi.     Price' 10  cents. 

21.  The  Lignites  of  the  Great  Sioux  Reservation;  a  Rejiort  on  the  Region  between  the  Grand 
and  Moreau  Rivers,  Dakota,  by  Bailey  Willis.     1885.     8°.     16  pp.     5  pi.     Price  5  cents. 

22.  On  New  Cretaceous  Fossils  from  California,  by  Charles  A.  White.  1885.  8°.  25  pp.  5  pi. 
Price  5  cents. 

23.  Observations  on  the  Junction  between  the  Eastern  Sandstone  and  the  Keweenaw  Series  on 
Keweenaw  Point,  Lake  Superior,  by  R.  D.  Irving  and  T.  C.  Chamberlin.  1885.  8°.  124  pp.  .  17  pi. 
Price  15  cents. 

24.  List  of  Marine  MoUusca,  comprising  the  Quaternary  Fossils  and  Recent  Forms  from  American 
Localities  between  Cape  Hatteras  and  Cape  Eoque,  including  the  Bermuda.s,  by  William  Healey  Dall. 

1885.  8^.     336  pp.     Price  25  cents. 

25.  The  Present  Technical  Condition  of  the  Steel  Industry  of  the  United  States,  by  Phiueas 
Barnes.     1885.     8°.     85  pp.     Price  10  cents. 

26.  Copper  Smelting,  by  Henry  M.  Howe.     1885.     8°.     107  pp.     Price  10  cents. 

27.  Report  of  Work  done  in  the  Division  of  Chemistry  aud  Physics,  mainly  during  the  Fiscal  Year 
1884-'85.     1886.     8°.     80  pp.     Price  10  cents. 

28.  The  Gabbros  and  Associated  Hornblende  Rocks  occurring  in  the  Neighborhood  of  Baltimore, 
Maryland,  by  George  Huntington  Williams.     1886.     8°.     78  pp.     4  pi.    Price  10  cents. 


IV  ADVERTISEMENT. 

29.  On  tbe  Fresli-AVater  Invex'tebrates  of  the  Nortli  American  Jurassic,  by  Charles  A.  AVbite.  1886. 
8^.     41  pp.     4  pi.     Price  5  cents. 

30.  Second  Contribution  to  the  Studies  on  the  Cambrian  Faunas  of  North  America,  by  Charles 
Doolittle  Walcott.     1886.     8°.     369  pp.     33  pi.     Price  2,5  cents. 

31.  Systematic  Review  of  our  Present  Knowledge  of  Fossil  Insects,  including  Myriapods  and 
Arachnids,  by  Samuel  Hubbard  Scudder.     1886.     8=.     128  pp.     Price  15  cents. 

32.  Lists  and  Analyses  of  the  Mineral  Springs  of  the  United  States;  a  Preliminary  Study,  by 
Albert  C.  Peale.     1886.     8°.     235  pp.     Price  20  (/ents. 

33.  Notes  on  the  Geology  of  Northern  California,  by  J.  S.Diller.     1886.    8°.    23  pp.    Price  5  cents. 

34.  On  till'  liclatiouoftheLaramieMoUuscauFaunato  that  of  the  Succeeding  Fresh-Water  Eocene 
and  Other  Gi(Mi|,N,  l,y  Charles  A.  White.     1886.     8^.     54  pp.     5  pi.     Price  lO.cents. 

'  35.  Plivsir;il  rnipi-rties  of  the  Iron-Carburets,  by  Carl  Barns  and  Vincent  Strouhal.  1886.  8-'. 
62  pp.     Price  10  cents. 

36.  Subsidenceof FineSolidParticlesinLiquids,byCaTlBarus.    1886.    8°.    58pp.    PricelOcents. 

37.  Types  of  the  Laramie  Flora,  by  Lester  F.  Ward.     1887.     8°.     354  pp.     57  pi.     Price  25  cents. 

38.  PeridotiteofElliottCounty,Kentucky, by  J.  S.Diller.     1887.     8^^.    31pp.    Ipl.    Price5cents. 

39.  The  Upper  Beaches  and  Deltas  of  the  Glacial  Lake  Agassiz,  bj'  Warren  Upham.  1887.  8°. 
84  pp.     1  pi.     Price  10  cents. 

40.  Changes  in  River  Courses  in  AVashington  Territory  due  to  Glaciation,  by  Bailey  Willis.  1887. 
8-^.     10  pp.     4  pi.     Price  5  cents. 

41.  On  the  Fossr.  Faunas  of  the  Upper  Devonian — the  Genesee  Section,  New  York,  by  Henry  S. 
AVillianis.     1887.     8°.     121  iip.     Ipl.     Price  15  cents. 

42.  Reportof  Work  (biiic  in  liic  1  >i\i>ioii  of  Chemistryand  Phy.sics,  mainly  during  the  Fiscal  Year 
1885-'86.     F.W.Clarke,  CliiciClMiiiiM.     1ns7.     8'-^.     1.52  pp.     1  pi."   Price  15  cents. 

43.  Tertiary  and  Cretaceous  Stiata  of  tlic  Tuscaloosa,  Tombigbee,  and  Alabama  Rivers,  by  Eugene 
A.  Smith  and  Lawrence  C.  .Johnson.     1887.     8^.     189  pp.     21  pi.     Price  15  cents. 

44.  Bibliography  of  North  American  Geology  for  1886,  by  Nelson  H.  Darton.  1887.  8°.  35  pp. 
Price  5  cents. 

45.  The  Present  Condition  of  Knowledge  of  the  Geology  of  Texas,  by  Robert  T.  Hill.  1887.  8°. 
94  pp.     Price  10  cents. 

46.  Nature  and  Origin  of  Deposits  of  Phosphate  of  Lime,  by  E.  A.  F.  Penrose,  jr.,  with  an  Intro- 
duction by  N.  S.  Shaler.     1888.     8°.     143  pp.     Price  15  cents. 

47.  Analyses  of  Waters  of  the  Yellowstone  National  Park,  with  an  Account  of  the  Methods  of 
Analysis  employed,  liy  Frank  Austin  Gooch  and  James  Edward  AVhitfield.  1888.  8°.  84  pp.  Price 
10  cents. 

48.  On  the  Form  and  Position  of  the  Sea  Level,  by  Robert  Simpson  AVoodward.  1888.  8"^.  88 
pp.     Price  10  cents. 

49.  Latitudes  and  Longitudes  of  Certain  Points  in  Missouri,  Kansas,  and  New  Mexico,  by  Robert 
Simpson  AA^oodward.     1889.     8^.     133  pp.     Price  15  cents. 

50.  Formulas  and  Taljles  to  Facilitate  the  Construction  and  Use  of  Maps,  by  Robert  Simpson 
AA^oodward.     1889.     8*^.     124  pp.     Price  15  cents. 

51.  On  Invertebrate  Fossils  from  the  Pacific  Coast,  by  Charles  Abiathar  AVhite.  1889.  8^^.  102 
pp.     14  pi.     Price  15  cents. 

52.  Subaerial  Decay  of  Rocks  and  Origin  of  the  Red  Color  of  Certain  Formations,  by  Israel 
Cook  Russell.     1889.     8°.     65  pp.     5  pi.     PricelOcents. 

53.  The  Geologv  of  Nantucket,  by  Nathaniel  Southgate  Shaler.  1889.  8'^.  55  pp.  10  pi.  Price 
10  cents. 

54.  On  the  Thermo-Electric  Measurement  of  High  Temperatures,  Ijy  Carl  Barns.  1889.  8°. 
313  pp.,  incl.  1  pi.     11  pi.     Price  25  cents. 

55.  Report  of  AVork  done  in  the  Division  of  Chemistry  and  Phvsics,  mainly  during  the  Fiscal 
Year  1886-'87.     Frank  AVigglesworth  Clarke.  Chief  Chemist.     1889.     8^.     96  pp.     Price  lO'cents. 

56.  Fossil  AVood  ancl  Lignite  of  the  Potomac  Formation,  by  Frank  Hall  Knowlton.  1889.  8^. 
72  pp.     7  pi.     Price  10  cents. 

57.  A  Geological  Reconnoissance  In  Southwestern  Kansas,  by  Robert  Hay.  1890.  8°.  49  pp. 
2  111.     Price  5  cents. 

58.  The  Glacial  Boundary  in  AVestern  Pennsylvania,  Ohio,  Kentucky,  Indiana,  and  Illinois,  by 
George  Frederick  AA'right,  with  an  Introduction  by  Thomas  Chrowder  Chamberlin.  1890.  8°.  112 
pp.,  incl.  1  pi.     8  pi.     Price  15  cents. 

59.  The  Galibros  .and  Associated  Rocks  in  Delaware,  by  Frederick  D.  Chester.  1890.  8°.  45 
pp.     1  pi.     Price  10  cents. 

60.  Report  of  AA'ork  done  in  the  Division  of  Chemistry  and  Physics,  mainly  during  the  Fiscal 
Year  1887-'88.     F.  W.  Clarke,  Chief  Chemist.     1890.     8°.     174  pp.     Price  15  cents. 

61.  Contributions  to  the  Mineralogy  of  the  Pacific  Coast,  by  William  Harlow  Melville  and  AA'^al- 
demar  Lindgreu.     1890.    8^.     40  pp.     3  pi.     Price  5  cents. 

62.  The  Greenstone  Schist  Areas  of  the  Menominee  and  Marquette  Regions  of  Michigan,  a  Con- 
tribution to  the  Subject  of  Dynamic  Metaraorphism  in  Eruptive  Rocks,  by  George  Huntington  AVilliams, 
with  an  Introduction  by  Roland  Duer  Ir\'ing.     1890.     8°.     241  pp.     16  pi.     Price  30  cents. 

63.  A  Bibliography  of  Paleozoic  Crustacea  from  1698  to  1889,  including  a  List  of  North  Amer- 
ican Species  and  a  Systematic  Arrangement  of  Genera,  by  Anthony  W.  Vogcles.  1890.  8^.  177  pp. 
Price  15  cents. 

64.  A  Report  of  AA''ork  done  in  the  Division  of  Chemistry  and  Physics,  mainly  during  the  Fiscal 
Year  1888- 89.     F.  AV.  Clarke,  Chief  Chemist.     1890.     8'-.     60  pp.     PricelOcents. 


ADVERTISEMENT.  V 

65.  Stratigraphy  of  the  Bituminous  Coal  Field  of  Penusvlvauia,  Ohio,  aucl  West  Virginia,  by 
Israel  C.  White.     1891.     8'^'.    212  pp.     11  pi.     Price  20  cents.       ' 

66.  On  a  Group  of  Volcanic  Eocks  from  the  Tewan  Mountains,  New  Mexico,  and  on  the  Occur- 
rence of  Primary  Quartz  in  Certain  Basalts,  by  Joseph  Paxson  Iddings.  1890.  8<^.  34  pp.  Price  5 
cents. 

67.  The  Relations  of  the  Traps  of  the  Newark  System  in  the  New  Jersey  Region,  by  Nelson 
Horatio  Darton.     1890.    8'^.    82  pp.    Price  10  cents. 

68.  Earthquakes  in  California  in  1889,  by  James  Edward  Keeler.  1890.  8^.  25  pp.  Price  5 
cents. 

69.  A  Classed  and  Annotated  Biography  of  Fossil  Insects,  by  Samuel  Howard  Scudder.  1890. 
8°.     101  pp      Price  15  cents. 

70.  A  Report  on  Astronomical  Work  of  1889  and  1890,  by  Robert  SLmpsou  Woodward.  1890.  8^^. 
79  pp.     Price  10  cents. 

71.  Index  to  the  Known  Fossil  Insects  of  the  World,  including  Myriapods  and  Arachnids,  by 
Samuel  Hubbard  Scudder.     1891.     8°.     744  pp.     Price  50  cents. 

72.  Altitudes  between  Lake  Superior  and  the  Rocky  Mountains,  by  Warren  Upham.  1891.  8^. 
229  px).     Price  20  cents. 

73.  The  Viscosity  of  Solids,  by  Carl  Barns.     1891.     8'-\     xii,  139  pp.     6  pi.     Price  15  cents. 

74.  The  Minerals  of  North  Carolina,  by  Frederick  Augustus  Genth.  1891.  8*^.  119  pp.  Price 
15  cents. 

75.  Record  of  North  American  Geology  for  J887  to  1889,  inclusive,  bv  Nelson  Horatio  Darton. 
1891.     8°.     173  pp.     Price  15  cents. 

76.  A  Dictionary  of  Altitudes  in  the  United  States  (Second  Edition),  compiled  by  Henry  Gannett, 
Chief  Topographer.     1891.     8"^.     393  pp.     Price  25  cents. 

77.  The  Texan  Permian  and  its  Mesozoic  Types  of  Fossils,  by  Charles  A.  White.  1891.  8°.  51 
pp.     4  pi.     Price  10  cents. 

78.  A  Report  of  Work  done  in  the  Division  of  Chemistry  and  Physics,  mainly  during  the  Fiscal 
Year  1889-'90.     F.  AV.  Clarke,  Chief  Chemist.     1891.     8".     131  pp.     Price  15  cents. 

79.  A  Late  Volcanic  Eruption  in  Northern  California  and  its  Peculiar  Lava,  by  J.  S.  Diller. 

80.  Correlation  Papers — Devonian  and  Carboniferous,  by  Henry  Shaler  Williams.  1891.  8°. 
279  pp.     Price  20  cents. 

81.  Correlation  Papers — Cambrian,  by  Charles  Doolittle  Walcott.  1891.  8°.  547  pp.  3  pi. 
Price  25  cents. 

82.  Correlation  Papers— Cretaceous,  by  Charles  A.  White.  1891.  8'^.  273  pp.  3  pi.  Price  20 
cents. 

83.  Correlation  Papers — Eocene,  by  William  Bullock  Clark.  1891.  8°.  173  pp.  2  pi.  Price 
15  cents. 

84.  Correlation  Papers— Neocene,  by  W.  H.  Dall  and  G.  D.  Harris.  1892.  8>=.  349  pp.  3  pi. 
Price  25  cents. 

85.  Correlation  Papers — The  Newark  System,  by  Israel  Cook  Russell.  1892.  8°.  344  pp.  13  pi. 
Price  25  cents. 

86.  Correlation  Papers— Archeau  and  Algonkian,  by  C.R.  Van  Plise.  1892.  8^\  ,549  pp.  12  pi. 
Price  25  cents. 

87.  A  Synopsis  of  American  Fossil.  Brachiopoda,  including  Bibliography  and  Synonymy,  by 
Charles  Schuchert.     1897.     8'-.     464  pp.     Price  30  cents. 

88.  The  Cretaceous  Foraminifera  of  New  Jersey,  by  Rufus  Mather  Bagg,  Jr.  1898.  8^.  89  pp. 
6  pi.     Price  10  cents. 

89.  Some  Lava  Flows  of  the  Western  Slope  of  the  Sierra  Nevada,  California,  by  F.  Leslie 
Ransome.     1898.     8°.     74  pp.     11  pi.     Price  15  cents. 

90.  A  Report  of  Work  done  in  the  Division  of  Chemistry  and  Physics,  mainly  during  the  Fiscal 
Year  1890-'91.     F.  W.  Clarke,  Chief  Chemist.     1892.     8^^.     77  pp.     Price  10  cents. 

91.  Record  of  North  American  Geology  for  1890,  by  NeLson  Horatio  Darton.  1891.  8°.  88  pp. 
Price  10  cents. 

92.  The  Compressibility  of  Liquids,  by  Carl  Barns.     1892.     8°.     96  pp.     29  pi.     Price  10  cents. 

93.  Some  Insects  of  Special  Interest  from  Florissant,  Colorado,  and  Other  Points  in  the  Tertiaries 
of  Colorado  and  Utah,  by  Samuel  Hubbard  Scudder.     1892.     8*^.     35  pp.     3  pi.     Price  5  cents. 

94.  The  Mechanism  of  Solid  Viscosity,  by  Carl  Barns.     1892.     8°.     138  pp.     Price  15  cents. 

95.  Earthquakes  in  California  in  1890  and  1891,  by  Edward  Singleton  Holden.  1892.  8°.  31pp. 
Price  5  cents. 

96.  The  Volume  Thermodynamics  of  Liquids,  by  Carl  Barus.     1892.     8-^.     100  pp.     Price  10  cents. 

97.  The  Mesozoic  Echinodermata  of  the  United  States,  by  W.B.  Clark.  1893.  8'^.  207  pp.  oOpl. 
Price  20  cents. 

98.  Flora  of  the  Outlying  Carboniferous  Basins  of  Southwestern  Missouri,  by  David  White. 
1893.     8^.     139  pp.     5  pi.     Price  15  cents. 

99.  Record  of  North  American  Geology  for  1891,  by  Nelson  Horatio  Darton.  1892.  8°.  73  pp. 
Price  10  cents. 

■    100.  Bibliography  and  Index  of  the  Publications  of  the  U.  S.  Geological  Survey,  1879-1892,  by 
Philip  Creveliug  Warman.     1893.     8-.     495  jip.     Price  25  cents. 

101.  Insect  Fauna  of  the  Rhode  Island  Coal  Field,  by  Samuel  Hubbard  Scudder.  1893.  8"^. 
27  pp.     2  pi.     Price  5  cents. 

102.  A  Catalogue  and  Bibliography  of  North  American  Mesozoic  Invertebrata,  by  Cornelius 
Breckinridge  Boyle.     1892.     8^.     315  pp.     Price  25  cents. 


VI  ADVERTISEMENT. 

103.  High  Temperature  Work  in  Igneous  Fusion  and  Ebullitiou,  chiefly  in  Relation  to  Pressure, 
hy  Carl  Barus.     1893.     8°.     57  pp.     9  pi.     Price  10  cents. 

104.  Glaciation  of  the  Yellowstone  Valley  north  of  the  Park,  by  Walter  Harvey  Weed.  1893.  8^. 
41  pp.     4  pi.     Price  5  cents. 

105.  The  Laramie  and  the  OA'erlying  Livingstone  Formation  in  Montana,  by  Walter  Harvey 
Weed,  with  Report  on  Flora,  by  Frank  Hall  Knowlton.     1893.     8^.     68  pp.     6  pi.     Price  10  cents. 

106.  The  Colorado  Formation  and  its  Invertebrate  Fauna,  by  T.  W.  Stanton.  1893.  8^.  288 
pp.     45  pi.     Price  20  cents. 

107.  The  Trap  Dikes  of  the  Lake  Champlain  Region,  by  James  Fnrman  Kemp  and  Vernon 
Freeman  Marsters.     1893.     8'-^.     62  pp.     4  pi.     Price  10  cents. 

108.  A  Geological  Reconnoissanoe  in  Central  AVashington,  by  Israel  Cook  Russell.  1893.  8-". 
108  pp.     12  pi.     Price  15  cents.  ' 

109.  The  Eruptive  and  Sedimeutary  Rocks  on  Pigeon  Point,  Minnesota,  and  their  Contact  Phe- 
nomena, by  William  Shirley  Bayley.     1893.     8".     121  pp.     16  pi.     Price  15  cents. 

110.  The  Paleozoic  Section  in  the  Vicinity  of  Three  Forks,  Montana,  by  Albert  Charles  Peale. 
893.     8°.     56  pp.     6  pi.     Price  10  cents. 

111.  Geology  of  the  Big  Stone  Gap  Coal  Fields  of  Virginia  and  Kentucky,  by  Marius  R.  Camp- 
bell.    1893.     8^.     106  pp.     6  pi.     Price  15  cents. 

112.  Earthquakes  in  California  in  1892,  by  Charles  D.  Perrine.    1893.    8^.    57  pp.    Price  10  cents. 

113.  A  Report  of  Work  done  in  the  Division  of  Chemistrv  during  the  Fiscal  Years  1891-'92  and 
1892-'93.     F.  W.  Clarke,  Chief  Chemist.     1893.     8°.     115  pp.     Price  15  cents. 

114.  Earthquakes  in  California  in  1893,  by  Charles  D.  Perrine.    1894.    8^.    23  pp.    Price  5  cents. 

115.  A  Geographic  Dictionary  of  Rhode  Island,  by  Henry  Gannett.  1894.  8°.  31  pp.  Price 
5  cents. 

116.  A  Geographic  Dictionary  of  Massachusetts,  by  Henry  Gannett.  1894.  8^.  126  pp.  Price 
15  cents. 

117.  A  Geographic  Dictiouai-y  of  Connecticut,  by  Henry  Gannett.  1894.  8°.  67  pp.  Price  10 
cents. 

118.  A  Geographic  Dictionary  of  New  Jersey,  by  Henry  Gannett.  1894.  8^.  131  pp.  Price  15 
cents. 

119.  A  Geological  Reconnoissance  in  Northwest  Wyoming,  by  George  Homans  Eldridge.  1894. 
8°.     72  pp.     Price  10  cents. 

120.  The  Devonian  System  of  Eastern  Pennyslvania  and  New  York,  by  Charles  S.  Prosser.  1894. 
8^.     81pp.     2  pi.     Price  10  cents. 

121.  A  Bibliography  of  North  American  Paleontology,  by  Charles  Rollin  Keyes.  1894.  8"^.  251 
pp.     Price  20  cents. 

122.  Results  of  Primary  Triangnlation,  by  Henry  Gannett.  1894.  8'^.  412  pp.  17  pi.  Price 
25  cents. 

123.  A  Dictionary  of  Geographic  Positions,  by  Henry  Gannett.  1895.  8°.  183  pp.  1  pi.  Price 
15  cents. 

124.  Revision  of  North  American  Fossil  Cockroaches,  by  Samuel  Hubbard  Scudder.  1895.  8^. 
176  pp.     12  pi.     Price  15  cents. 

125.  The  Constitution  of  the  Silicates,  by  Frank  Wigglesworth  Clarke.  1895.  8^=.  109  pp. 
Price  15  cents. 

126.  A  Mineralogical  Lexicon  of  Franklin,  Hampshire,  and  Hampden  counties,  Massachnsetts, 
by  Benjamin  Kendall  Emerson.     1895.     8^.     180  pp.     1  pi.     Price  15  cents. 

127.  Catalogue  and  Index  of  Contributions  to  North  American  Geology,  1732-1891,  by  Nelson 
Horatio  Darton.     1896.     8°.     1045  pp.     Price  60  cents. 

128.  The  Bear  River  Formation  and  its  Characteristic  Fauna,  by  Charles  A.  White.  1895.  8^. 
108  pp.     11  pi.     Price  15  cents. 

129.  Earthquakes  in  California  in  1894,  by  Charles  D.  Perrine.    1895.     8^~.     25  pp.     Price  5  cents. 

130.  Bibliography  and  Index  of  North  American  Geology,  Paleontology,  Petrology,  and  Miner- 
alogy for  1892  and  1893,  by  Fred  Boughton  Weeks.     1896.     8-\     210  pp.     Price  20  cents. ' 

131.  Report  of  Progress  of  the  Division  of  Hydrography  for  the  Calendar  Years  1893  and  1894, 
by  Frederick  Haynes  Newell,  Topographer  in  Charge.     1895.     8°.     126  pp.     Price  15  cents. 

132.  The  Disseminated  Lead  Ores  of  Southeastern  Missouri,  by  Arthur  Wiuslow.  1896.  8°. 
31  pp.     Price  5  cents. 

133.  Contributions  to  the  Cretaceous  Paleontology  of  the  Pacific  Coast:  The  Fauna  of  the 
Knoxville  Beds,  by  T.  W.  .Stanton.     1895.    8-\     132  pp.     20  pi.     Price  15  cents. 

134.  The  Cambrian  Rocks  of  Pennsylvania,  by  Charles  Doolittle  Walcott.  1896.  8°.  43  pp. 
15  pi.     Price  5  cents. 

135.  Bibliography  and  Index  of  North  American  Geology,  Paleontology,  Petrology,  and  Miner- 
alogy for  the  Y'ear  1894,  by  F.  B.  Weeks.     1896.     8*^.     141  pp.     Price  15  cents.' 

136.  Volcanic  Rocks  of  South  Mountain,  Pennsylvania,  by  Florence  Bascom.  1896.  8'^.  124  pp. 
28  pi.     Price  15  cents. 

137.  The  Geology  of  the  Fort  Riley  Military  Reservation  and  Vicinity,  Kansas,  by  Robert  Hay. 
1896.     8°.     35  pp.     8  p'l.     Price  5  cents. 

138.  Artesian-Well  Prospects  in  the  Atlantic  Coastal  Plain  Region,  by  N.  H.  Darton.  1896.  8"^. 
228  pp.     19  pi.     Price  20  cents. 

139  Geology  of  the  Castle  Mountain  Mining  District,  Montana,  by  W.  H.  Weed  and  L.  V.  Pirs- 
son.     1896.     8°.     164  pp.     17  pi.     Price  15  cents. 

140.  Report  of  Progress  of  the  Division  of  Hydrography  for  the  Calendar  Year  1895,  by  Frederick 
Haynes  Newell,  Hydrographer  in  Charge.     1896.     8"^.     356  pp.     Price  25  cents. 


ADVERTISEMEIs^T.  VII 

Ul.  The  Eocene  Deposits  of  tlie  Middle  Atlantic  Slope  in  Delaware,  Maryland,  and  Virginia, 
1)T  William  Bullock  Clark.     1896.     8°.     167  pp.     40  pi.     Price  15  cents. 

142  A  Brief  Contribution  to  the  Geology  and  Paleontology  of  Northwestern  Louisiana,  by 
T.  Wayland  Vaughan.     1896.     8°.     65  pp.     4  pi.     Price  10  cents  ,^nn      o->      -,-,, 

143.  A  Bibliography  of  Clays  and  the  Ceramic  Arts,  by  John  C.  Branner.     1896.     8^.     114  pp. 

144.  The  Moraines  of  the  Missouri  Coteau  and  their  Attendant  Deposits,  by  James  Edward  Todd. 
1896.     8°.     71  pp.     21  pi.     Price  10  cents. 

145.  The  Potomac  Formation  in  Virginia,  by  W.  M.  Fontaine.     1896.     8^.     149  pp.     2  pi.     Price 

146.  Bibliography  and  Index  of  North  American  Geology,  Paleontology,  Petrology,  and  Miner- 
alooy  for'the  Year  1895,  by  F.  B.  AVeeks.     1896.     8'\     130  pp.     Price  15. cents. 

°    147.  Earthquakes  in  California  in  1895,  by  Charles  D.  Perrine,  Assistant  Astronomer  in  Chargo 
of  Earthquake  Observations  at  the  Lick  Observatory.     1896.     8'-.     23  pp.     Price  5  cents. 

148  Analyses  of  Rocks,  with  a  Chapter  on  Analytical  Methods,  Laboratory  of  the  United  States 
Geological  Survey,  1880  to  1896,  by  F.  W.  Clarke  and  W.  F.  Hilleljraud.     1897.     8^^.     306  pp.     Price 

149.  Bibliography  and  Index  of  North  American  Geology,  Paleontology,  Petrology,  and  Miner- 
alogy for  the  Year  1896,  by  Fred  Boughton  Weeks.     1897.     8°.     152  pp.     Price  15  cents. 

150.  The  Educational  Series  of  Rock  Specimens  collected  and  distributed  by  the  United  States 
Geological  Survey,  bv  Joseph  Silas  Diller.     1898.     8°.     398  pp.     47  pL     Price  25  cents. 

151.  The  Lower  Cretaceous  Gryphicas  of  the  Texas  Region,  by  R.  T.  Hill  and  T.  Wayland 
Vaughan.     1898.     8°.     139  pp.     25  pi.     Price  15  cents. 

152.  A  Catalogue  of  the  Cretaceous  and  Tertiary  Plants  of  North  America,  by  F.  H.  Knowlton. 
1898.     8°.     247  pp.     Price  20  cents. 

153.  A  Bibliographic  Index  of  North  American  Carboniferous  Invertebrates,  by  Stuart  Weller. 
1898.     8°.    653  pp.     Price  35  cents. 

154.  A  Gazetteer  of  Kansas,  by  Henry  Gannett.     1898.     8°.     246  pp.     6  pi.     Price  20  cents. 

155.  Earthquakes  in  California  in  1896  and  1897,  by  Charles  D.  Perrine,  Assistant  Astronomer 
in  Charge  of  Earthquake  Observations  at  the  Lick  Observatory.     1898.     8°.     47  pp.     Price  5  cents. 

156.  Bibliography  and  Index  of  North  American  Geologj',  Paleontology,  Petrology,  and  Miner- 
alogy for  the  Y'ear  1897,  by  Fred  Boughton  Weeks.     1898.     8^.     130  pp.     Price  15  cents. 

160.  A  Dictionary  of  Altitudes  in  the  United  States  (Third  Edition),  compiled  by  Henry 
Gannett.     1899.     8^.     775  pp.     Price  40  cents. 

161.  Earthquakes  in  California  in  1898,  by  Charles  D.  Perrine,  Assistant  Astronomer  in  Charge 
of  Earthquake  Observations  at  the  Lick  Observatory.     1899.     8°.     31pp.     1  pi.     Price  5  cents. 

Ill  preparation:  ^     ,      „   ,_ 

157.  The  Gneisses,  Gabbro-Schists,  and  Associated  Rocks  of  Southeastern  Minnesota,  by  C.  W. 

158.  The  Moraines  of  southeastern  South  Dakota  and  their  Attendant  Deposits,  by  J.  E.  Todd. 

159.  The  Geology  of  Eastern  Berkshire  County,  Massachusetts,  by  B.  K.  Emerson. 

WATER-SUPPLY  AND  IRRIGATION  PAPERS. 

By  act  of  Congress  approved  June  11,  1896,  the  following  provision  was  made: 
"Propidecl,  That  hereafter  the  reports  of  the  Geological  Survey  in  relation  to  the  gauging  of 
streams  and  to  the  methods  of  utilizing  the  water  resources  may  be  priu'ed  in  octavo  form,  not  to 
exceed  one  hundred  pages  in  length  and  live  thousand  copies  in  number ;  oue  thousand  copies  of  which 
shall  be  for  the  ofiflciaruse  of  the  C4eological  Survey,  one  thousand  five  hundred  copies  shall  be  deliv- 
ered to  the  Senate,  and  two  thousand  five  hundred  copies  shall  be  delivered  to  the  House  of  Repre- 
sentatives, for  distribution." 

Under  this  law  the  following  papers  have  been  issued: 

1.  Pumping  Water  for  Irrigation,  by  Herbert  M.  ^"  ilson.     1896.     8-^.     57  pp.     9  pi. 

2.  Irrigation  near  Phtt'uix,  Arizona,' by  Arthur  P.  Davis.     1897.     8°.    97  pp.     31  pi. 

3.  Sewage  Irrigation,  bv  George  W.  Rafter.     1897.     8^.     100  pp.     4  pi. 

4.  A  Reconnoissance  in  Southeastern  Washington,  by  Israel  Cook  Russell.    1897.    8°.    96  pp.    7  pi. 

5.  Irrigation  Practice  on  the  Great  Plains,  by  Elias  Branson  Cowgill.     1897.     8^.     39  pp.     12  pi. 

6.  Underground  Waters  of  Southwestern  Kansas,  by  Erasmus  Haworth.    1897.    8°.    65  pp.    12  pi. 

7.  Seepage  Waters  of  Northern  Utah,  by  Samuel  Fortier.     1897.     8°.    50  pp.     3  pi. 

8.  Windmills  for  Irrigation,  by  Edward  Charles  Murphy.     1897.     8^.     49  pp.    8  pi. 

9.  Irrigation  near  Greeley,  Colorado,  by  David  Boyd.     1897.     8'=.     90  pp.    21  pi. 

10.  Irrigation  in  Mesilla  Valley,  New  Mexico,  by  F.  C.  Barker.     1898.    8°.     51  pp.     11  pi. 

11.  River  Heights  for  1896,  by  Arthur  P.  Davis.     1897.     8*^.     100  pp. 

12.  Water  Resources  of  Southeastern  Nebraska,  by  Nelson  H.  Darton.    1898.     8°.     55  pp.     21  pL 

13.  Irrigation  Systems  in  Texas,  by  William  Ferguson  Hutson.     1898.     8^''.     67  pp.     10  pi. 

14.  New  Tests  of  Certain  Pumps  and  AVater-Lifts  used  in  Irrigation,  by  Ozni  P.  Hood.  1889.  8°. 
91  pp.    1  pi. 

15.  Operations  at  River  Stations,  1897,  Part  I.     1898.     8'^.     100  pp. 

16.  Operations  at  River  Stations,  1897,  Part  II.     1898.    8^.     101-200  pp. 

17.  Irrigation  near  Bakersfield,  California,  by  C.  E.  Grunsky.     1898.     8°.     96  pp.     16  pi. 

18.  Irrigation  near  Fresno,  California,  by  C.  E.  Grunsky.     1898.     8°.     94  pp.     14  pi. 

19.  Irrigation  near  Merced,  California,  by  C.  E.  Grunsky.     1899.     8°.     59  pp.     11  pi. 

20.  Experiments  with  Windmills,  by  T.  O.  Perry.     1899.     8°.    97  pp.     12  pi. 


VIII 


ADVEETISEMF.NT. 


21.  Wells  of  Northern  Intliana,  by  Frank  Leverett.      1899.     8°.     82  pp.     2  pi. 

22.  Sowase  Irrigation,  Part  II,  by  George  AV.  Kaiter.     1899.     8--".     100  pp.     7  pi. 

23.  Water-Right  Problems  of  Bighorn  Mountains,  by  Elwood  Mead.     1899.     8"^.     62  pp.     7  pi. 

24.  Water  Eesonrces  of  the  State  of  New  York,  Part  I,  by  George  \V.  Rafter.  1899.  8°. 
99pp.     13  pi. 

25.  Water  Resources  of  the  State  of  New  York,  Part  II,  by  George  W.  Rafter.  1899.  8°. 
101-200  pp.     12  pi. 

26.  Wells  of  Southern  Indiana  (Continuation  of  No.  21),  by  Frank  Leverett.     1899.     8^.     64  pp. 

In  ijress: 

27.  Operations  at  River  Stations,  1898,  Part  I.     1899.     8-=.     100  pp. 

28.  Operations  at  River  Stations,  1898,  Part  II.     1899.     8^.     101-200  pp. 

In  preparation : 

29.  Wells  and  Windmills  in  Nebraska,  by  Edwin  H.  Barbour. 

30.  Water  Resources  of  the  Lower  Peninsula  of  Michigan,  by  Alfred  C.  Lane. 

TOPOGRAPHIC  MAP  OF  THE  UNITED  STATES. 

When,  in  1882,  the  Geological  Survey  was  directed  by  law  to  make  a  geologic  map  of  the  United 
States  there  was  in  existence  no  suitable  topographic  map  to  serve  as  a  base  for  the  geologic  map. 
The  preparation  of  such  a  topogi-.iphic  map  was  therefore  immediately  begun.  About  one-fifth  of  the 
area  of  the  country,  excluding  Alaska,  has  now  been  thus  mapped.  The  map  is  published  in  atlas 
sheets,  each  sheet  representing  a  small  quadrangular  district,  as  explained  under  the  next  head- 
ing. The  separate  sheets  are  sold  at  5  cents  each  when  fewer  than  100  copies  are  purchased,  but  when 
they  are  ordered  in  lots  of  100  or  more  copies,  whether  of  the  same  sheet  or  of  dilferent  sheets,  the 
price  is  2  cents  each.  The  mapped  areas  are  widely  scattered,  nearly  every  State  being  represented. 
About  900  sheets  have  been  engraved  and  printed;  they  are  tabulated  by  States  in  the  Survey's 
"List  of  Publications,"  a  pamphlet  which  may  be  had  on  application. 

The  map  sheets  represent  a  great  variety  of  topographic  features,  and  with  the  aid  of  descriptive 
text  they  can  be  used  to  illustrate  topographic  forms.  This  has  led  to  the  projection  of  an  educational 
series  of  topographic  folios,  for  use  wherever  geography  is  taught  in  high  schools,  academies,  and 
colleges.     Of  this  series  the  first  folio  has  been  issued,  viz: 

1.  Physiographic  types,  by  Henry  Gannett,  1898,  folio,  consisting  of  the  following  sheets  and  4 
Images  of  descriptive  text:  p'argo  (N.  Dak.-Minn.),  a  region  in  youth;  Charleston  (W.Va.),a  region  in 
maturity;  Caldwell  (Kans.),  a  region  in  old  age;  Palmyra  (Va.),  a  rejuvenated  region ;  Mount  Shasta, 
(Cal.),  a  young  volcanic  mountain;  Eagle  (Wis.),  moraines;  Sun  Prairie  (Wis.),  drumlins;  Donald- 
sonville  (La.),  river  flood  plains;  Boothbay  (Me.),  a  fiord  coast;  Atlantic  City  (N.  J.),  a  barrier-beach 
coast. 

GEOLOGIC  ATLAS  OF  THE  UNITED  STATES. 

The  Geologic  Atlas  of  the  United  States  is  the  final  form  of  publication  of  the  topographic  and 
geologic  maps.  The  atlas  is  issued  in  parts,  progressively  as  the  surveys  are  extended,  and  is  designed 
ultimately  to  cover  the  entire  country. 

Under  the  plan  adopted  the  entire  area  of  the  country  is  divided  into  small  rectangular  districts 
(designated  quadrangles),  bounded  by  certain  meridians  and  jiarallels.  The  unit  of  survey  is  also  the 
unit  of  publication,  and  the  maps  and  descriptions  of  each  rectangular  district  are  issued  as  a  folio  of 
the  Geologic  Atlas. 

Each  folio  contains  topographic,  geologic,  economic,  and  structural  maps,  together  with  textual 
descriptions  and  explanations,  and  is  designated  by  the  name  of  a  principal  town  or  of  a  prominent 
natural  feature  withiu  the  district. 

Two  forms  of  issue  have  been  adopted,  a  "library  edition"  and  a  "field  edition."  In  both  the 
sheets  are  bound  between  heavy  i^aper  covers,  but  the  library  copies  are  permanently  bound,  while 
the  sheets  and  covers  of  the  field  copies  are  only  temporarily  wired  together. 

Under  the  law  a  copy  of  each  folio  is  sent  to  certain  public  libraries  and  educational  institu- 
tions. The  remainder  are  sold  at  25  cents  each,  except  such  as  contain  an  unusual  amount  of  matter, 
which  are  priced  accordingly.  Prepayment  is  obligator}'.  The  folios  ready  for  distribution  are  listed 
below. 


No. 

I^ame  of  sheet. 

State. 

Limiting  meridians. 

Limiting  parallels. 

A.rea,  in 
square 
miles. 

Price, 
cents. 

Montana 

/Georgia 

110°-H1° 

\                           85°-So°  30' 

120°  30'-121° 

84°  3U'-85o 

1210-121°  30' 

850-85°  30' 

105°-105°  30' 

85°  30'-86° 

106°  45'-107°  15' 

1                           77°  30'-78° 

4d°-46° 
34°  30'-35° 
38°  30'-39° 
35°  30'-36° 
38°  30'-39° 
35°-35°  30' 
38°  30'-39° 
35°-35°  30' 
38°  45'-39o 

390-39°  30' 

3,354 
98U 
932 
969 
932 
975 
932 
975 
465 

925 

0- 

25 
25 

t 

California 

Tennessee 

California 

Tennessee 

Colorado 

Tennessee 

Colorado 

(Virginia 

West  Virginia.. 
iKaryland 

i\ 

25 

25 

6 

7 

Cliattauooga 

Pikes  Peak  (out  of  stock) 

25 
25 
25 

9 
10 

Anthracite-Crested  Butte 

Harpers  Ferry 

50 
25 

ADVERTISEMENT. 


Limitins  meridians 


Limiting  parallels 


Area,  ir 
square 
miles. 


Prici', 
cents. 


Jackson  ... 
Estillville  , 


Fredericksburg. 

Staunton 

Lassen  Peak 

Knoxville 


Stevenson  ... 

Cleveland 

Pikeville 

McMinnville. 
Noniini 


26  I  Pocahontas . 

27  iloiTistovrn. 

28  Piedmont... 


California 

(Virginia 
Kentucky 
Tennessee 

/Maryland 

\Yirginia 

/Virginia 

tWest  Virginia. 

California 

Tennessee 

Korth  Carolina 

California 

California 

(Alabama 

•^Georgia 

(Tennessee 

Tennessee 

Tennessee 

Tennessee 

/Maryland 


Montana. 


(iSrevadaCitv.i 

Nevada  City ...  { Grass  YalleV . 

(Banner  Hili  .J 

fGallatin  . 

/Yellowstone    Na-  I  Canyon.. 

\\    tional  Park.  ) Shoshone 

[Lake.... 

Pyramid  Peak 

'  Franklin 

BriceviUe 

Buckbannon 

Gadsden 

Pneblo 

Downieville 

Butte  Special 

Truckee 

■VYartburg 

Sonora 


W- 


43  Bid  well  Ba 

44  I  Tazewell.. 


Boise 

Kicbraond 

London  

Tenmile  District  Special. 
Roseburg 

Hoi  yoke 


California 

/■Virginia 

\West  Virginia  . 

Tennessee 

West  Virginia 

Alabama 

Colorado 

California 

Montana 

California 

Tennessee 

California 

California" !!!.'.' 

/Virginia 

nv est  Virginia. 

Idaho 

Kentucky 

Kentucky 

Colorado 


120°  30'-121o 
820  30'-83° 
770-77°  30' 
79°-79°  30' 


84°  30'-85° 
850-85°  30' 
850  30'_S6o 


00'  25"-121o  03'  45" 
'  01'  35"-121°  05'  04" 
57'  05"-121o  00'  25" 


120°-120o  30' 
■90-790  30' 


1040  30'-105o 

120°  30'-121° 

20'  30"-112°  36'  42" 

1200-120°  30' 

84°  30'-85° 
1200-120°  30' 
1000-100°  30' 
1210-121°  30' 

81°  30'-82° 
1160-1160  30' 

840-84°  30' 

S4°-84o  30' 

106°  8'-106o  16' 

1230-1230  30' 

720  30'-73° 


38°-38°  30' 
36°  30'-37° 


3SO-38°  30' 

40°-41° 

350  30'-36° 


350-350  30' 
35°  30'-36° 
35°  30'-36° 


39°  13'  50"-39"  17'  16" 
390  10'  22"-39°  13'  50" 
390  13'  60"-39o  17'  16" 


38°  30'-39° 
38°  30'-39o 
360-36°  30' 
38°  30'-39o 
340-340  30' 
380-38°  30' 
39°  30'-40° 
450  59'  28"-46o  02'  54" 
39°-39°  30' 
360-36°  30' 
370  30'-38o 
29°  30'-30o 
39°  30'-40° 


0-37°  30' 


11.65 
12.09 
11.65 


STATISTICAL  PAPERS. 

Mineral  Resources  of  the  United  States  [1882],  by  Albert  Williams,  jr.  1883.  8^.  xvii813iip. 
Price  50  cents.  '  '  ' 

Mineral  Resources  of  the  United  States,  1883  and  1884,  bv  Albert  AVilliams,  ir.  188.5  8°  xiv 
1016  pp.     Price  60  cents.  '  j  •  , 

Mineral  Resources  of  the  United  States,  1885.  Division  of  Mining  Statistics  and  Technolooy 
1886.     8°.     vii,  576  pp.     Price  40  cents. 

Mineral  Resources  of  the  United  States,  1886,  by  David  T.  Day.  1887.  8°.  viii,  813  pp.  Price 
60  cents. 

Mineral  Resources  of  the  United  State.s,  1887,  by  David  T.  Day.  1888.  8'^.  vii,  832  pp.  Price 
50  cents. 

Mineral  Resources  of  the  United  States,  1888,  by  David  T.  Day.  1890.  8'='.  vii,  652  pp.  Price 
50  cents. 

Mineral  Resources  of  the  United  States,  1889  and  1890,  by  David  T.  Day.  1892.  8'='.  viii,  671  pp. 
Price  50  cents. 

Jliueral  Resources  of  the  United  States,  1891,  by  David  T.  Day.     1893.     8^.     vii,  630  pp.    Price 


X  ADVERTISEMENT. 

Mineral  Resources  of  the  United  States,  1892,  by  DaTid  T.  Day.  1893  8=.  vii,  850  pp.  Price 
50  cents. 

Mineral  Resources  of  the  United  States,  1893,  by  David  T.  Day.  1894.  8°.  viii,  810  pp.  Price 
50  cents. 

On  March  2, 1895,  the  following  provision  was  included  in  an  act  of  Congress: 

"Provided,  That  hereafter  the  report  of  the  mineral  resources  of  the  United  States  shall  be 
issued  as  a  part  of  the  report  of  the  Director  of  the  Geological  Survey." 

In  compliance  veith  this  legislation  the  following  reports  have  been  published : 

Mineral  Resources  of  the  United  States,  1894,  David  T.  Day,  Chief  of  Division.  1895.  8°.  xv, 
646  pp.,  23  pi. ;  xix,  735  pp.,  6  pi.     Being  Parts  III  and  IV  of  the  Sixteenth  Annual  Report. 

Mineral  Resources  of  the  United  States,  1895,  David  T.  Day,  Chief  of  Division.  1896.  8°. 
xxiii,  542  pp.,  8  pi.  and  maps;  iii,  .543-1058  pp.,  9-13  pi.  Being  Part  III  (in  2  vols.)  of  the  Seventeenth 
Annual  Report. 

Mineral  Resources  of  the  United  States,  1896,  David  T.  Day,  Chief  of  Division.  1897.  8°. 
xii,  642  pp.,  1  pi. ;  643-1400  pp.     Being  Part  V  (in  2  vols.)  of  the  Nineteenth  Annual  Report. 

Mineral  Resources  of  the  United  States,  1897,  David  T.  Day,  Chief  of  Division.  1898.  8°. 
viii,  651  pp.,  11  pi. ;  viii,  706  pp.     Being  Part  VI  (in  2  vols.)  of  the  Nineteenth  Annuaf  Report. 

The  money  received  from  the  sale  of  the  Survey  publications  is  deposited  in  the  Treasury,  and 
the  Secretary  of  that  Department  declines  to  receive  bank  checks,  drafts,  or  postage  stamps ;  all  remit- 
tances, therefore,  must  be  by  money  order,  made  payable  to  the  Director  of  the  United  States 
Geological  Survey,  or  in  currency — the  exact  amount.  Correspondence  relating  to  the  publications 
of  the  Survey  should  be  addressed  to 

The  Director, 

United  States  Geological  Survey, 
Washington,  D.  C,  June,  1S99.  Washington,  D.  C. 


[  Take  this  leaf  out  and  paste  the  separated  titles  upon  three  of  your  cata- 
logue cards.  The  first  and  second  titles  need  no  addition ;  over  the  third  write 
that  subject  under  which  you  would  place  the  hook  in  your  library.] 


LIBRARY  CATALOGUE  SLIPS. 

United  States.     Department  of  the  interior.     {U.  S.  geological  survey.) 
Department  of  the  interior  |  —  |  Monograplis  |  of  tlie  |  United 
States  geological  snrvej'  |  Volume  XXXIII  |  [Seal  of  the  depart- 
ment] I 
Washington  |  government  printing  office  |  1899 
Second    title:   United    States   geological   survey  |   Charles   D. 
Walcott,  director  |  —  |  Geology  |  of  the  |  Narragansett  basin  | 
by  I  N.  S.  Shaler,  J.  B.  Woodworth,  and  A.  F.  Foerste  |   [Vig- 
nette] I 

Washington  |  go\erunient  printing  office  |  1899 
i°.     xx,  402  pp.    31  Jil. 


Shaler  (N.  S.),  "Woodworth  (J.  B.),  and  Foerste  (A.  F.) 

United    States   geological  'survey    |    Charles   D.  "VValcott,   di- 
rector  |  —  |  Geology  |  of  the  |  Karragansett  basin  |  by  |  N.  S.  i 

Shaler,  J.  B.  Woodworth,  and  A.  F.  Foerste  |  [Vignette]  | 

Washington  |  government  printing  office  |  1899 

4P.    XX,  402  pp.    31  pi. 

[United  States.    Department  of   ttie  interior.     {TT.  S.  geological  survei/.) 
Monograph  XXXIII.]  • 

1 
i 
United   States   geological   survey   |    Charles   D.   Walcott,   di-  | 

rector  |  —  |  Geology   |   of  the  |  Narragansett  basin  1  by  |  K.  S.  ' 

Shaler,  J.  B.  Woodworth,  and  A.  F.  Foerste  |  [Vignette]  | 
Washington  |  government  printing  office  |  1899 
i°.    xvii,  402  pp.    31  pi. 

[United  States.    Dejmrtment   of   the  intcHor.     [U.  *S. 
Monograph  XXXni.] 


77G2   230 


iJifiDINS  CO     " 

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